Help with slow stations because of data ( this is what I think)

Can someone help me understand what could cause this?

I'm still learning SQL and only taking basic courses right now. We have a machine connected to a MES system and a PLC. In one station there is a CHECK IN step, and sometimes a CHECK OUT step, where the MES trigger is executed.

Every few months (maybe every 3 or 4 months), the machine cycle time becomes about 1 or 2 seconds slower during those steps. The machine still runs, but it is noticeably slower than normal.

What is strange is that the Chinese engineers who built the machine connect remotely and do something in SQL or the database, and after that the cycle time goes back to normal. This has happened several times.

I know this is probably not enough information to find the exact problem, but I would like to understand what kinds of things could cause this. Could it be related to indexes, large tables, locks, database maintenance, or communication between the MES and SQL?

I'm asking because I will probably be responsible for supporting these systems in the future, and I'm trying to learn more about how SQL affects MES and PLC systems.

Any ideas would be appreciated.