ESP8266 create another WiFiClientSecure always fail https request - esp8266

Question

I have some ESP8266 and ESP32.
I use them with a MQTT (SSL) server and a web server.
I use two WiFiClientSecure to avoid to be disconnected to my MQTT server.
One WiFiClientSecure instance is dedicate to the MQTT server and the other one to HTTPS requests
The ESP32 works well, I can connect to my MQTT server and send HTTPS request without issue.
The ESP8266 (Wemos d1 mini) doesn't work as expected. The HTTPS request always fail.
It only works if I only use one instance of WiFiClientSecure. However during the HTTPS request I am disconnected of the MQTT server.
Is this behavior is due to hardware limitation ?
Here is the revelant part of code
WiFiClientSecure espClient;
WiFiClientSecure espClient2;
PubSubClient mqttClient(espClient);
const char* rootCABuff = \
"-----BEGIN CERTIFICATE-----\n" \
...
"-----END CERTIFICATE-----\n";
void setup() {
/* Connect to wifi then set cert*/
espClient.setCACert(rootCABuff);
espClient2.setCACert(rootCABuff);
/* Define clock or will fail*/
setClock();
...
client.setServer("myserver", myport); // MQTT server
...
}
void loop() {
...
if (!mqttclient.connected()) {
reconnect();
}
else
{
mqttclient.loop();
}
...
/*Sometimes a https request is needed*/
HTTPClient http;
http.setTimeout(10000);
char* baserequest = "https://myserver.com";
httpRequestData="somedata";
Serial.print("[HTTPS] begin...\n");
if (http.begin(espClient2, baserequest)) { // HTTPS
http.addHeader("Accept", "application/json");
http.addHeader("Content-Type", "application/x-www-form-urlencoded");
Serial.print("[HTTPS] POST...\n");
int httpCode = http.POST(httpRequestData);
http.end();
} else {
Serial.printf("[HTTPS] Unable to connect\n");
}
...
}