I actually raised the concern of big break in time for studying foreign language due to Mod System at CSW when I visited. One of their long-time language teachers said “we find it is fine, and we just review if we need to” It seemed like they just dealt with the learning loss and didn’t seem to have put much thought into that issue, I assume as other benefits of the system are good. There was no “bridge” system that they shared.
I am not necessarily pro or con for Mod system, it is wonderful for some things, not so good for others and will entirely depend on how implemented! I have had people warn me off it depending on kids learning styles, and highly recommend it for other kids…