I just finished a run where for a while, even after visiting Tao and using Boris to go from Gola to Pupsville, I couldn't use Boris to go to Gola Highlands. I managed to fix it by talking to Boris and exiting out without traveling. I lost enough time to that that it (maybe) killed sub-3, so this is as much a question (does anyone know what causes this?) as a point of warning.

I can't say I've run into anything of the sort before... finding a glitch is kinda exciting though, I don't think we know of any that are consequential other than the Henry's Bag thingo petriform found (unsure if some other small ones have been found though, or if someone else found that before petriform).

On the specifics: do you know when it started? Was the option on the menu not there or did selecting the option not work? Anything that might seem... exploitable I guess?

My condolences for missing sub-3 as well. :<

I visit Tao at 1:43:20 (1:40:56 on the timer), use Boris to go from Gola to Pupsville at 1:44:20 (1:41:56), and then at 1:45:25 (1:43:01) I try to use Boris to go back to Gola and it doesn't show up on the list. Not sure how this glitch would be useful at all unless there was a way to reverse-engineer it to get to certain areas early.

This is pretty puzzling; you did everything right and I don't see why on earth the game wouldn't give you the unlock. I can look into replicating the circumstances and see if I can find anything out, but right now I really have no idea.

In any case I'm sorry that it hindered your run

In hindsight I probably should have selected the spot where Gola Highlands would be on the list, but I didn't quite know where that was and didn't want to waste any more time. If it happen again I'll report back here!