In my mobile build FPS starts with 60 fps fixed but around 2 to 3 minutes fps drops first to 45 then to 32 in a test map with no mesh at all only my character and a box.
I use statfile profiler to check the usage and it shows lots of PoolThereads with high ms counts for much more detail you can take my profiler data from here:
https://drive.google.com/open?id=1G6420IqXN4Nwq-s93yrmXoFI-u7FwGGs
Most of my ms used by:
FFileTransferRunnable with 250 ms fixed
FMessageBus.Router with 100ms fixed
Sometimes FPS Drops More And Most Thread Names Coused This Problem With Ms Usages Are:
TaskGraphThreadNP 3 = 25014 ms
TaskGraphThreadHP 7 = 25010 ms
TaskGraphThreadHP 6 =24997 ms
TaskGraphThreadBP 11 =24997 ms
TaskGraphThreadBP 10 =24997 ms
TaskGraphThreadBP 9 =24997 ms
TaskGraphThreadNP 2 =2500 ms
TaskGraphThreadHP 5 =2040 ms
TaskGraphThreadBP 8 =973ms