Ugh, I feel you! I was dealing with the same "why does my facebook keep saying session expired" issue last week. Turns out, it was a problem with my VPN. If you’re using one, try disabling it and see if that helps.
Also, check if your Facebook app is updated. Sometimes the older versions glitch out. Hope this works for you!
Also, check if your Facebook app is updated. Sometimes the older versions glitch out. Hope this works for you!