I would like to add what I'm experiencing with my phone to this topic.
First, why the date added sorting method is important to me : I have several artists that have released albums on the same year, but these albums names are not in alphabetical order. What this causes is wrong sorting for these albums (as what I would like to achieve is release date sorting, which is what makes the most sense for me). In previous version of Poweramp, I achieved this using the date added sorting method.
Since Poweramp does not support the full release time tag (which allows for full Year/Month/Day release date tagging), and that file-system sorting is not possible when using non folder-hierarchy views, the only way to achieve correct sorting is using date added sorting (when using music library views).
Now, coming into Poweramp V3, I am 300% sure this sorting method is currently broken, and this bug persists even on reinstalls and complete rescans (I have even completely purged all my music files three times from my SD card to try and fix this, to no avail).
To make sure of this, I have used a script to edit my last date modified info on all my music files. They currently are 100% in order in this regard (each song is marked as being last modified one hour apart each).
I have confirmed this using the SE Explorer app that does indeed achieve the correct sorting of music files when using the last date modified sorting in their app. This should prove that at least, in my case, my last date modified info is valid and not equal to null or such.
Now to the bug present in Poweramp. As stated by Oscarwho210, Poweramp seems to currently order using an unknown sorting method when using last date modified sorting. What I'm currently experiencing, is what would seemingly be alphabetical sorting in song list views, and what I would assume, be a broken/random sorting method when in album list views. In album view specifically, sometimes I get correct sorting, sometimes reversed sorting, and sometimes completely out of order sorting. It doesn't seem to follow alphabetical ordering.
What's more, disabling the option for using file system last date modified times (and using scanner first seen time) does not change ordering at all. Albums and songs will get ordered just the same as last time, even on full rescans, which makes me wonder what info is Poweramp currently using when using this sorting method, as it seems to be broken both when using scanner first seen times and file system last modified times.
And adding to this, using the reverse toggle when using date added sorting does absolutely nothing at all. If this is not a bug, it is very confusing as the toggle does not get disabled. Also, if it is intentional and not a bug, please enable this option again, as it is an useful option to have.
This issue has persisted for months, and is even present on two different phones (with the same sorting being displayed on both phones). For information, my phones are Oneplus 5 and Nokia 8.1.
I had already opened another topic on this issue but it apparently was ignored. So please, look into this issue. I am certain something is wrong.