I feel like this has been going on for several versions now. My setting for Default sort for comments is Top, but when I open a post, the sorting method appears to be Hot instead. The image in the post shows what a typical post looks like for me when I open it.
I hesitate to call this a bug right now, as last time I had a problem like this it was user error, so I'm not discounting some conflicting setting that I've overlooked.
It seems to be working fine for me in v1.0.307. This problem was fixed in 1.0.303 so if you're on an earlier version, you should update the app.
If you're on a later version than that but still having this problem, can you post a bug report? To do that, go into Settings and tap on the three dots in the top right. Then on Report Bug. You can submit that or just reply to your post and add the info here. Mainly, the settings info after the steps to reproduce part will be helpful.
This was the problem, though I don't know how I ended up in the situation I was in, as I was stuck on v1.0.301. When I checked the Google Play Store after seeing your comment, there was no update available, and the app page still had v1.0.301 as the latest version. I had no reason to suspect that my app was out-of-date until your post.
For posterity, I also had to join and then leave the beta program before v1.0.309 became available.
I don't think I've seen that but I'll know what to do now if there's a problem with receiving a Play Store update.