Disappearing levels and clouds

Hi,
I use Unreal Engine 4.25, and Unreal is fabulous so far however, in the past 1 month always some issue happen when open a saved scene. For example whole levels are just disappearing. Secondly, parts of the levels are disappearing completely like Clouds. While it is hard time to rebuild all these things again and again I would like to ask if any solution for the disappearing content.
I kindly watched all UE Forum threads so far for example to find a emergency save Level Map ,b ut nothing so far.
Is anything happened to Unreal Engine 4 that made it became extremely laggy and unreliable now?
So far it is my favourite software in terms of stability, so should I simply update to newer versions? Because I chose this 4.25 as the others were really unstable.
Thanks,