Thanks for the details @rojin
Funnily enough this sounds exactly like Logstash execption in pipeline worker where @badger also responded and pointed to ConcurrentModificationException · Issue #19 · ip2location/logstash-filter-ip2location · GitHub where it was suggested to try version 2.1.2. of ip2location. You seem to be using a previous version here so I'd give updating a try.
Not hearing back on that previous issue could well mean that this resolved the problem back then.
I had seen this issue initially and now that you also use ip2location, and on the same Elastic stack version, it seems that this might indeed be fitting. It can be hard at times to select the correct parts of a message to search for related issues and, as I mentioned on Slack, more information upfront is always helpful. Had you initially mentioned that this plugin was used and on what version, I would have directly suggested to look in that direction.
Have a great weekend, all!