I had and solved the problem you described - working with Brandmeister direction and not working with DMRGateway selected and any DMR network enabled.
This has me pulling my hair out for several days :/
I discovered that in the DMRGateway mode there was a problem initializing the MMDVM. I found this by watching live log and keeping this open in a separate browser while I made changes to the config. Everything worked fine, but it would hang trying to initialize and then it would log failed after 6 tries to initialize. If you would switch back it would work.
I reflashed using pistar-mmdvmhshatflash, and the MMDVM was able to initialize without issue. VERY STRANGE indeed.
Maybe this will work for you.
73s and GL
Help with DMR issues