Resource translations no longer applied x time after installation - asp.net-mvc

Question

I've been tasked with making an update to an existing asp core mvc site. I had to add a filter to an existing report.
The site uses resource files for string translations.
After uploading the site to the server, the site is running, everything is fine. the site runs under a different port for test purposes than the live site.
The moment my colleague tests the site, the site shows with it's keys only.
When i check immediatly after, for me as well, no resource strings are shown, only the keys.
Restarting IIS doesn't help. The only thing that temporarily works, is copying the files again from my computer to the server. Then the translation strings work again. Untill they don't.
I have no clue as what could be the cause and i am looking for ideas to check.
The current things i want to confirm is, when it reverts to keys, if the .resources.dll is still there. Although the virus scanner logs don't show activity, and the production site which is on the same server doesn't expoerince this problem, sepite having the same .resources.dll.
If you think knowing the startup.cs might be helpfull, let me know, or if someone thinks 'if i could only know that', just give out a shout. All input is welcome. It's difficult for me now to know what info could be usefull and what not. Posting a link to the whole reporsitory isn't really an option for me. I hope you understand.
EDIT 2021/02/23
Added a redacted startup.cs
Personal progress, it's not the wrong language it's picking up rather then it's showing the resource keys after x time. The resource keys happen to be in english. It's as if the french resource dll gets deleted, but only infor the test version of the site.
using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
...
using DevExpress.AspNetCore;
using Microsoft.AspNetCore.Authentication.Cookies;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Localization;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Razor;
using Microsoft.AspNetCore.Routing;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.FileProviders;
namespace ...
{
public class Startup
{
private const string Loginpath = "";
public static string LiveUrl { get; set; }
public IConfiguration Configuration { get; }
public IHostingEnvironment HostingEnvironment { get; }
private RequestLocalizationOptions SiteLocalizationOptions { get; }
public Startup(IConfiguration configuration, IHostingEnvironment env)
{
IList<CultureInfo> supportedCultures = new List<CultureInfo>
{
// new CultureInfo("en-US"),
new CultureInfo("fr-FR"),
};
SiteLocalizationOptions = new RequestLocalizationOptions()
{
DefaultRequestCulture = new RequestCulture("fr-FR"),
SupportedCultures = supportedCultures,
SupportedUICultures = supportedCultures
};
//the third culture provider looks at the browsers preferenced culture. When the first visitor give english as prefered language, somehow parts of the site become english for subsequent all visitors.
//at some point there was an english site option, and artifacts of that remain throughout the code.
//clearing the providers should force the site to always use English.
SiteLocalizationOptions.RequestCultureProviders.Clear();
HostingEnvironment = env;
...
}
// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
services.Configure<CookiePolicyOptions>(options =>
{
// This lambda determines whether user consent for non-essential cookies is needed for a given request.
options.CheckConsentNeeded = context => true;
options.MinimumSameSitePolicy = SameSiteMode.None;
});
//Add localization and translations
services.AddLocalization(options => options.ResourcesPath = "Resources");
services.Configure<RequestLocalizationOptions>(options =>
{
options.SupportedCultures = SiteLocalizationOptions.SupportedCultures;
options.SupportedUICultures = SiteLocalizationOptions.SupportedUICultures;
options.DefaultRequestCulture = SiteLocalizationOptions.DefaultRequestCulture;
});
services.AddDevExpressControls();
services.AddMvc().AddJsonOptions(options => options.SerializerSettings.ContractResolver = new Newtonsoft.Json.Serialization.DefaultContractResolver())
.AddViewLocalization(LanguageViewLocationExpanderFormat.Suffix)
.AddDataAnnotationsLocalization(options =>
{
options.DataAnnotationLocalizerProvider = (type, factory) => factory.Create(typeof(SiteResource));
})
.AddJsonOptions(options => options.SerializerSettings.ContractResolver = new Newtonsoft.Json.Serialization.DefaultContractResolver())
.SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme)
.AddCookie(options => options.LoginPath = new PathString(Loginpath));
...
//config
...
services.Configure<DatabaseSettings>(Configuration.GetSection("Database"));
services.Configure<HtmlPageSettings>(Configuration.GetSection("HtmlPages"));
services.Configure<ReportSettings>(Configuration.GetSection("Reporting"));
services.Configure<FilesSettings>(Configuration.GetSection("Files"));
services.Configure<AdminSettings>(Configuration.GetSection("Administrator"));
LatContext.ConnectionString = ...;
CroContext.ConnectionString = ...;
if (HostingEnvironment.IsDevelopment())
{
//repositories
services.AddSingleton<IUserRepository, UserRepository>();
services.AddSingleton<IStoredProcedures, StoredProcedures>();
//services
services.AddScoped<ILoginService, LoginService>();
}
else if (HostingEnvironment.IsEnvironment("Mock"))
{
//repositories
//No need to add repositories, since they are not used when the services are mocked
//services
services.AddScoped<ILoginService, MockLoginService>();
}
else //production
{
//repositories
services.AddSingleton<IUserRepository, UserRepository>();
services.AddSingleton<IStoredProcedures, StoredProcedures>();
//services
services.AddScoped<ILoginService, LoginService>();
}
}
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else if (env.IsEnvironment("Mock"))
{
}
else //production
{
app.UseExceptionHandler("/Home/Error");
// The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
app.UseHsts();
}
app.UseHttpsRedirection();
app.UseDefaultFiles();
app.UseStaticFiles();
//app.UseStaticFiles(new StaticFileOptions
//{
// FileProvider = new PhysicalFileProvider(Path.Combine(env.ContentRootPath, "node_modules")),
// RequestPath = "/node_modules"
//});
app.UseCookiePolicy();
app.UseAuthentication();
app.UseRequestLocalization(SiteLocalizationOptions);
...
app.UseDevExpressControls();
app.UseMvc(mvcRoutes =>
{
...
});
}
}
}