I think there is a problem with the ACYMailing /language/en-GB/en-GB.com_acym.ini language file in the JA Tour Quickstart package for Joomla 5.
I was trying to change some of the JA Tour template text like "Tour Plan" using Joomla's built in Language Overrides, but when I do a search on the Site language files I'm not getting any results. I looked at the cache that's created in the "_overrider" table and it's incomplete. It consistently stops creating rows once it hits the en-GB.com_acym.ini file. Once I deleted that file, the cache created 5252 rows as opposed to 609 rows. Then I get search results for Tour Plan.
My quickstart package was from last month, so I just downloaded the latest JA Tour Quickstart package for Joomla 5 and tested it again today on a fresh installation and I have the same problem. The _overrider table is only 592 rows until I delete en-GB.com_acym.ini, then it creates 3002 rows. I'm working on a local copy on Xampp but I was hoping you could look into it.