Hi,
Unfortunately UEFN’s Memory and pre-submission tesing functionality can still be very broken. Myself and many others had issues where the Memory Calculation button would be greyed out until we changed the play mode type (use the 3 dots where the green play button is in the viewport).
If this isn’t related to that, you may either have too many spawn devices or if you’re doing the memory calculation while being in-game, that will put strain on the server and loading.
Remember to also be in Edit mode when doing the memory calcuation and making any changes, not Play mode.
Can you post a screenshot of the error? These issues are usually tied to memory and, in UEFN’s case, the mode you’re using. Just would like to see whether it’s an execution failure related to packaging and unreal revision or memory.
Each project should also be backed up. Unlike Unreal, UEFN isn’t very reliable only using it locally since you can’t merge or transfer files to Unreal.