[Design]-Unable to add new anchor points to path in XD.

I'm having an odd problem with one of the paths I've created in a recent project. I can remove, manipulate, and otherwise play with the anchor points on this path, but for some reason I can't add any new ones, whether I try double-clicking on the path or using the pen tool. My other paths work fine, and this one was working fine awhile ago.

I've tried closing and re-opening the program, duplicating and then deleting the original path, turning off layers, reorganizing layers, etc. Is there some weird setting I'm missing? It's bizarre that this one path would be immune to new points.

I attached a video of what happens when I try.

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