Hello there.
First and foremost, amazing program !
Really, it's the most complete and practical of its kind in the appstore.

Now to the bugs:
1- If you merge two layers inside a group they merge with the opacity of the group. That is not a problem if the group its at 100% opacity, but if its less, it's a problem.
An example of this: make a group with 3 layers; the group at %50 opacity; the layers at 100%; merge 2 layers; the resulting layer its at 50% (the layer menu says 100% but you see the change) inside the group that already its at 50%.

2- Sometimes if you touch the screen fast it duplicates your last stroke. Its a random thing.

3- The undo with 2 fingers frequently makes a move or a zoom instead. Maybe it's a tolerance thing in the gesture or my fat fingers

Now to the suggestions:
1- Like others have voted, a Floating / permanent color wheel would be amazing

2- Speaking of color wheel, HSL with color wheel at the same time.

3- A Quick menu / pie menu / tool box or some other way of fast access to selected tools.

4- Easier access to the secondary color of the brush.

5- Better reading in layer menu. ¿Color tagging or more visual offset of masks layers and clipping layers maybe?

Oki-doki.
That's it.
Thanks for the constant updates and involvement with the program.
Cheers.