Maybe some padding got increased slightly so that the total height of the dash would not fit into the maximum allowed height for the dash (15% of the screen height). This then would cause gnome-shell to try smaller and smaller icons until it fits.
Something like env MUTTER_DEBUG_DUMMY_MODE_SPECS="2560x1600@60.0" MUTTER_DEBUG_DUMMY_MONITOR_SCALES="2" dbus-run-session gnome-shell --wayland --nested can be used to test this on smaller screens (with super + drag to move the window around).
I'm not too sure here, the padding styles on the dash on main are not that different from 45 and experimenting around on my end with removing them doesn't seem to yield results similar to 45.
The trouble is a bunch of extraneous padding is included because of the need to make the area below the actual icons clickable which is contributing unseen height to the dash items... ideally not having to do this in the stylesheet with padding would be nice.
Oh yeah, that would be the culprit. I forgot about this, no wonder I was getting no where with the stylesheet. I'll revert that and re-adjust the stylesheet in a MR since it doesn't need all the padding I've added.