I can only suggest typical troubleshooting stuffs:
clear all app data/app cache (requires reauthentication to instances)
logout/login to all instances (if you didn’t clear app cache and app data)
disable any kind of third-party task manager (those don’t really do much anyway.)
temporarily disable third-party ad filters (many apps absolutely hate local SSL proxies/local VPNs. For me, Connect is unusable with AdGuard’s SSL filter, but it could be a general Lemmy issue)
Try and get crash logs. (This is a convoluted process on Android, so you will need to research a process that works for your phone. If someone has a point-n-shoot process for this, I really want to know.)
Different post display settings might reduce memory consumption. This is a theory, and I don’t know whch ones would have the biggest impact.
Connect will consume a considerable amount of phone memory, but it’s less than my average for other apps. It is currently using ~400MB RAM, but it peaks at ~1.5GB. I am also a heavy user, so there is that. (My app cache is only at about 500MB, for now.)