While you check the column definition for Track - have you ticked "Numeric"?
And if so, does toggling that setting help?
And just to complete the information: the field track is supposed to be numeric and only the slash is allowed as non-numeric character ... Taking the standard literally, would mean that track "numbers" with A and B (and so on) are in fact invalid track numbers.
Something else must be in place here. Something in the last update must have broken this. I have been having issues with this since @Florian changed the default behavior from numeric to as it was entered on discogs in 2018. It has slowly and inevitably it has gotten harder to use MP3TAGS to tag files ripped from vinyl. Discogs Track number for Vinyl to MP3 - Support - Mp3tag Community
I'm not a power MP3TAG user and only end up here when I think somethings broken. I have not changed my PC in a couple of years, chceking the customize columns, it seems that both %track% has been dropped, and Numeric set on somehow during the recent update or via some other issue.
This does not hurt but eventually, it does not improve the sorting.
If you want to keep the numeric sorting, you could do something to transform the alphabetic part into a number.
So if you set
Sort by: $replace(%track%,A,$ord(A),B,$ord(B),C,$ord(C),D,$ord(D))
then A01 leads to 6501 as the A has the character code 65.
All files with letters at the front will then appear apart from the plain numbers