Coming in late because I just discovered this myself. I added something to My List on my Ultra downstairs; upstairs on the old trusty Roku 3, My List is not refreshing and showing it.
What I did was switch profiles. It took forever to switch profiles over, and then it took forever to switch profiles back to mine. But once switched, My List was complete on the 3 like it was on the Ultra.
Netflix would do well to add a Refresh button, if nothing else. But they do offer the refresh feature; it's done by switching profiles [or, as others have pointed out, power cycling the Roku].
On my previous Fire TV Box, sometimes I had to fix similar glitches by force stopping the app and going back into it. I know that's because they're using the Android OS, but it was a handy feature. Now I'm going to put the onus onto the Roku team to offer something similar. If the app developer has screwed up, at least give me--the Roku user--a Roku-level control for stopping and restarting the app, as opposed to the entire Roku.