Hi,
JanusGraph keeps a record of open instances that sometimes is not updated properly. You can clean it with the methods here:
https://docs.janusgraph.org/advanced-topics/recovery/#janusgraph-instance-failure

Maybe it is no problem if your graph is dropped entirely, so you can also check:
https://docs.janusgraph.org/basics/common-questions/#dropping-a-database
After dropping, the graph can be recreated with the right configs.

Best wishes,     Marc