Keep being told “Your session has expired” when it hasn’t

Each time I have tried to post a question here, or respond to someone’s answer, I have to go through multiple re-sign-ins, yet I am and remain signed in.

The message I type, when I am finished writing, becomes highlighted in pink and a message says words to the effect, “Your session has expired” and another says I my message can’t be sent and I must try again later. “Later” never works. Multiple re-sign-ins (I’ve had to do as many as 10 or 12) are required. I persist just to see if anything will be revealed as to why this is happening, but “nada”. Every now and then, suddenly the system will allow my message to be sent.

Any ideas, anyone?