Unfortunately its failing on that branch as well with the same error. I will look into it later today or tomorrow and see if I can find out why it suddenly started throwing out that error. Definitely seems to be related to the allocator used in that one test. @lucian303 is correct that commenting out line 161 that calls shrink to fit is a workaround (although that might cause the test to fail)
I have found a fix for the issue and created a PR into tracktion engine.
Thanks very much. Fixed here: rpallocator: Added comparison operators to fix issues with newer co… · Tracktion/tracktion_engine@edd6fb6 · GitHub