This seems related to this.
I wonder if I have the same issue, as a Windows 10 machine on the same network can check in and out without problem in Unreal.
So after reading this, I created a symlink from /usr/bin/svn to the Binaries/Thirdparty/svn folder mentioned, but that didn’t unfortunately make a difference for me.
In that folder, there already was a Subversion.tps which doesn’t seem to do much…