I've been having this issue with my S9+. I just got off a tech support chat with Samsung and they walked me through these steps which has fixed my issues completely so far.
1. Power down phone
2. Hold the volume up and bixby button down then press the power button
3. when the android screen comes up let go of all 3 buttons
4. this will put the phone into android recovery
5. using the volume down button highlight "wipe cache partition" and press the power button to select
6. using the volume down button highlight "yes" and push the power button
7. press the power button again to reboot now.
This has worked great for me so far and has actually sped up my phone functioning quite a bit. I can now share to messenger from any website or app I've tried. I hope this helps. I am not tech savvy so I have no idea what happened during the last update to cause this issue but it is now fixed on my phone. Best luck.