“Unfortunately”, it seems to be ok, so your issue likely has nothing to do with this. Just in case, you can try the following but don’t expect too much:
EDIT: I’ve tried to compare a lot of packages and env vars between my working UM 17.10 and a liveCD but so far, no luck in finding what makes Dropbox work on my system…
Just to be sure, I’ve just tried to reinstall UM 17.04 in a VM and perform an upgrade to 17.10. Caja-dropbox is still functional that way (I installed it when on 17.04, before doing the upgrade, if that matters).
I wanted to check that the fact that it works on my main system didn’t come from a random package I installed at some point (I tried a few DEs on my PC, so there might still be packages or settings related to something else than MATE). It doesn’t seem to be the case.
The next step would be to thoroughly compare a fresh 17.10 install with the 17.04 upgraded to 17.10. Difference in packages installed and eventually the various settings.
Is it on a newly installed UM 17.10 or upgraded from 17.04? Asking this because that’s indeed the way it’s supposed to fix the issue but it doesn’t seem to work on a fresh 17.10 install (last time I checked, maybe it’s been fixed).
For the time being I downloaded nautilus drop box and the indicator icon works. With caja drop box I had an indicator icon but it wouldn’t produce a drop down menu when clicked. It would work in Ubuntu Mate 17.04 but didn’t in 17.10. I upgraded Mate online, took around 45 min, not bad.