If Bumble keeps crashing when you open a chat, close it all the way (on Android, go to Settings > Apps > Bumble > Force Stop; on iOS, swipe it off your list of recently used apps) and then open it again. This usually fixes a memory glitch or a hidden process that won't move.
Next, make sure you have the most recent version of Bumble installed from the app store on your device. Also, make sure the operating system on your phone is up to date, as old software often leads to crashes.
If the problem still happens, go to Settings > Apps > Bumble > Storage > Clear Cache on Android and clear the app's cache. Also, make sure that any VPN or battery-saving mode is turned off, as these can get in the way of chat.
These are key solutions that we can offer. If you have more, please share.