On these machines, you need to completely uninstall the service, and also uninstall all .net framework components, and do a fresh installation. First install .NET 4.7, reboot the system, then install NAV CU19 from the product DVD. This is actually what helped us lately in such situations
Answers
CU18 and CU19 cause the same mysterious abstract error on about 40% of our systems. CU17 is working fine.
Following errors are logged
We've contacted Microsoft. They have confirmed that it is a known issue with CU19 (and 18?).
We'll stick to CU17 until the issue is resolved..
And then I found this post. It just needs the .NET 4.7
Thanks for sharing @RemkoD