Roumigi53 Could this be related to the construction work happening between 3rd and 6th September?
Ah I see… this is even VERY likely! As that last B 312 bus stretch (which I’d just like to emphasize once again) is operated by the local Grindelwald Bus company, they might be the root cause of the issue, i.e. by currently feeding incomplete or incorrect data to SBB. Because currently you also can’t even buy that B 312 bus ticket separately, while other tickets for routes operated by them such as Grindelwald - Grosse Scheidegg still work as usual.
As the issue currently occurs with ANY arbitrary departure station (not just Basel), one could expect that this would be solved by until Sep 3rd latest.
So relax and just get that ticket on the 5th, when you’re absolutely sure you’ll make the trip (no falling sick or other change of plans). You may not realize that such point-to-point tickets do never “sell out” (see e.g. for today), and the price won’t change neither.