I haven’t found the root cause, but in all cases, CTRL+SPACE works. This isn’t the best, but light years better than nothing at all.
(this shortcut is not one I’ve used in the past, so this is likely standard behavior, but…) If you’re at the dot Model. and autocomplete list disappears, CTRL+SPACE consistently brings it back up, and when it does come back, it stays! If there’s only one possible autocomplete member, it’ll auto-fill the member for you upon CTRL+SPACE