Removing a host with some reports (say 200), and each of them with several log lines (10000) generates 2.000.000 DELETE sql statements in the same transaction.
More often than not, ActiveRecord won't be able to make such a big transaction, in fact it will likely eat all memory available and Foreman will stop working in that host. In the best scenario the DB will end up with a non-committed giant transaction.

I suggest deleting hosts and reports manually on host destroy to avoid this.