I have resolved this problem. I installed Brainsuite ver 19b, as well as the required MATLAB Runtime R2019b. Now svreg is working fine again.
I don’t have a clear idea of why it is now working, but I’m wondering if it could have something to do with having multiple MatLab Runtime versions installed, in addition to the full Matlab development environment (of yet a different version). I’m not aware of how the svreg code selects which Matlab environment to execute within — if it has to do with the order in which the different versions appear in the system PATH list, that could explain it. However, I tried messing with the order in the PATH variable and I couldn’t really reproduce the problem with ver 19b. So… who knows. I’m just happy it’s working again!