If the problems were caused by issues in the old Element Android (or Schildichat) app then yes - the Element X rewrite will likely fix it. It supports UnifiedPush, so if you're self-hosting a push gateway it should nicely integrate (as does Schildichat Next).
If the problem was in your push infrastructure, then the new app won't fix anything - however, UnifiedPush should be reliable these days (especially if you host your own instance; some of the shared ones are overloaded and/or deliberately throttle Matrix push). FCM obviously should be reliable too.
If the problem was in your push infrastructure, then the new app won't fix anything - however, UnifiedPush should be reliable these days (especially if you host your own instance; some of the shared ones are overloaded and/or deliberately throttle Matrix push). FCM obviously should be reliable too.