Why isn't Google Maps synching bookmarks?

Since the past 2 weeks or so, my Google Maps has stopped synching the bookmarks (stars) from web Google Maps. So far, erasing cache and rebooting haven't helped. The only fix is to erase data and reboot.

Any idea what's causing this and how I could fix it?

I'm using a Xperia Z3 Compact, on Slimm ROM 6.0.1 1.9 (MM).