Thanks for reaching out for assistance. I will be happy to help assist with resolving the problems you are experiencing on your Gallery app.
My first recommendation was going to be clearing the cache and data, but seeing as that didn't help. The next step you can try to do is force stopping the operation temporarily on the gallery app.
Follow these steps below:
Open settings > Apps > More Settings > Select show system apps > Gallery > Force Stop.
After doing this and if the symptoms persist, there are two other things that could be causing this to occur.
1. Software update. Check your device to make sure it's completely up-to-date with the latest software. This link here will help guide you on updating your phone: https://www.samsung.com/us/support/answer/ANS00077582/
2. Third party application (Try your phone in safe mode, to see if the gallery app is still crashing. If it is still crashing a factory data reset is recommended, if not, and it works perfectly, it's a third party application. Slowly remove apps from your device until you find which one is the culprit.)
If you have any other inquiries, feel free to reach out to the community or private message a moderator directly. We're always here for you!
