It is most likely several requests are handled at the same time and all got stuck at the hanged GenServer call. 5 seconds timeout happened and they all error out.
I find it very peculiar in the way you use the GenServer and ETS. you seems to be dynamically creating GenServer based on an external (webhook) originated batch_id? This is very vulnerable for malicious traffic.
And all the GenServer store some data in a shared ETS table using the batch_id as the key? (is is a set, bag or something else?) Why do you need the ETS, you can just keep the batch in the GenServer,
