Not sure why that happened, but just simply resize it first by pulling the left edge over a bit, then reposition the tab bar. Might have to do that a couple of times to see the right edge, but once you do, you can use the magnet.
That is unusual and while I work with tabs daily, this not something I have encountered in any version of InDesign.
However, I also don't select a frame to format the contents. Instead, I work with the text within. For example, I would set up two paragraph styles: one for the wine name/price and a second for the description, and then set the tabs for the styles themselves. If you move to that approach, I suspect that will solve this issue, but I'm happy to look at your file if you just need a clear answer.