The heart icon overlay that appears when under the comfort effect does not display correctly with the Overflowing Bars mod.

After looking into the code for Overflowing Bars, it seems the mod cancels every other health overlay when it is installed, by interrupting the event after its setup. This is done most likely to avoid visual mismatches, since it fundamentally changes Health Boost to no longer stack bars vertically.

There isn't much I can do here. Overflowing Bars would have to tweak their implementation somehow, and disable the event interrupt.