[13:04:11] [Server thread/DEBUG]: Level "MyWorld" took 103.4ms, setting tick rate to 2 ticks [13:04:11] [Server thread/DEBUG]: Raising level "MyWorld" tick rate to 1 ticks
TPS for the server is usually set at 20, which is 50ms per tick. When pocketmine takes longer than 50ms to complete processing for a given level, the tick rate for the level changes to compensate. If a level is taking that long to update then I'd guess that either something is wrong, or your server is very busy.