Well, mine is always mounted when launching Tweaks. Looks like the plot thickens...ive had the same issue countless times and have cone to a potential theory..
every time mine goes mental and luna restarts the device ive noticed over time that the active jail for tweaks which is typically noticable when using Tailor, is not there anymore, can you maybe run Tailor, get the message about "danger will robinson thar be jails active" etc and scroll far bottom, you should have your media/internal possibly /media/ext3fs if u made an ubuntu partition etc, possibly /opt and im guessing your entry for tweaks will be missing?
i'm purely guessing as mines always gone when tweaks starts doing reboots every launch, and removing then installing doesnt get the jail entry back.
normally there should be a line in tailor that reads
USB (Media) /var/palm/jail/org.webosinternals.tweaks.prefs/media/internal
pictture/attachment enclosed of a "normal" condition.
if you could check and see if you also have the same issue then maybe that can help solve it, if you dont then it at least eliminates my longshot theory (which doesnt help me the next time i get the problem again).