Hi,
I’m not sure about answering, cause I have not the solution actually, but I have a very similar installation and it runs fine, so maybe I can help you somehow.
I have recently updated to 3.4, currently running 3.4.0.9 and I’m using Immersion Theme. I am using a child theme, with original Immersion works fine also.
I am using Immersion 1.1.2.3 release, downloaded from Github and installed through FTP:
https://github.com/pkp/immersion/releases/tag/v1_1_2-3
Are you using that version?
Install a theme through the Gallery or through FTP should be the same, I just explain the steps I followed just in case you want to try.
Kike