I have same problem I think, although client is in linux
When trying to set up the account in the client 1st run wizard (or afterwards using the ‘add account’ option) on my new Manjaro installation I can’t connect to local server on my network if using local address - it gives same error as you get, even though I check the ‘trust this certificate anyway’ box, AND I have added the entry to my hosts file.
However, all works if using external address (but is so bloody slow!)
Client version: 2.5.1-2
However, the client is still working on my other dual boot installed OS - Xubuntu 18.04.1, although I dont have to go through the 1st time wizard as it has been set up for some time.
I think these bugs are relevant but dont have much of an idea
So, not very helpful, but at least you are not alone!