I need some confirmation of this from other players, but I noticed 2 problems since last night on item tooltips when comparing changes from upgrading items in quality and also when equipping items.
All of this was in the gamepad UI on PC on a High Elf templar with the racial 9% magicka recovery bonus.

First, upgrading items in quality shows a decrease in value each upgrade. White to green quality shows lower stats for all set bonuses, and possibly weapon damage also.
I specifically tested this on a Whitestrake's Retribution staff at the Rivenspire Westwind Lighthouse woodworking station where it was crafted.
I noticed though that this bug just seems to be that the set stats are listed on the wrong side of the screen, flipped, so that it looks like a decrease but attempting another upgrade shows the higher numbers from the previous upgrade screen being the lowest on the new screen. So the upgrade works but looks backwards.

Second and much bigger more complicated bug, he tooltip preview in the inventory showing how equipping an item will affect your stats is very bugged showing incorrect values. Not only this, but the end value of how it affects my stats is apparently very off.
Without any equipment, my base recovery is 616 with the racial, which seems off considering my unbuffed stamina recovery is 514 which should be the same as unbuffed magicka recovery making that 560 instead of 616. I also have rings and a necklace that each buff magicka recovery by 169, which buffed 9% by the racial would be 184. Those rings and necklace are purple Bahraha's Curse set with max magicka bonus 840 each and the typical set bonuses of 1164 max health then 1058 max magicka then 1058 max stamina.
I go to the inventory, completely naked still, and highlight the necklace, or a ring, and the preview of stat changes comes up showing the magicka recovery will change from 616 to 1008, 392 higher. That is definitely not right. Equip that necklace or ring and then check the character sheet and the actual value ends up as 819, which is a 203 increase instead of 169 or 184. The magicka recovery bonus from my racial seems to be a lot higher than 9% or the calculation is very off.
Equip the necklace or second ring and the stat then changes, but not just the magicka recovery incorrect. Tooltip shows max magicka increase from 16302 to 17226, which is correctly 840 increased by 10%, but the final equipped value is 17410. That's 184 extra max magicka that came from nowhere. The magicka recovery bonus preview shows increase from 819 to 1210, change of 391, but actual increase to 1022, change of 203 again. Also here, the set bonus shows incorrect actual increase. The tooltip preview is correct showing max health going from 15178 base to 16342, change of 1164, but the actual final value without any buffs shows 16574, an extra 232 over the 1164 buff from the set.
The final jewelry piece has the same 169 magicka recovery and 840 max magicka with the 1058 max magicka set bonus. This shows a tooltip preview change from 1022 recovery and 17410 max magicka and 16574 health to 1413 recovery and 19497 max magicka and health unchanged. Again, that is listing likely changes of 391 increased recovery and 2087 increase to magicka. The actual ending values are 1225 recovery and 19916 max magicka and health unchanged. That change is actually 203 increased recovery and 2506 increased max magicka.

So, tooltips are incorrect and the end value is also incorrect. This is definitely true for magicka recovery as nothing is expected to change that beyond my 9% passive.

Max magicka and health are different though as I am champion 565. That would mean 20% increase to each from champion points. The tooltip change previews don't take this into account, and even if they did they wouldn't tell us the reason why the number is what it is. (I miss games actually explaining things so we didn't have to know everything as good as the devs to figure it out. That would avoid uninformed bug reports.)
But going by the Champion Points 20% max stat boost, max at 20% at cp300, that would make the 840 max magicka increase 1008 which is lower than the end value increases at the second jewelry of 1108, 16302 to 17410, and much lower than the 3rd jewelry increase by 2506 even when you subtract the 20% buffed set bonus of 1058 that equals 1269.2 to get 1236.4 increase instead of 1008.
If we apply the 20% to the magicka recovery, which isn't supposed to, it still doesn't account for the change from 169 with 9% buff to 184 that then goes to 203. If the 20% did buff it then it would end up either 221 or 218.
At least, the max health does follow the correct rule, but that's apparently because no item trait buffs or enchantments affected it. I have not yet tested the heavy armor passive buffs to stats.
Champion passive increases do help to explain the changes to certain stats, but the values of enchantments and traits and final values are not correct and they aren't supposed to affect magicka recovery or anything except max magicka/health/stamina.


Tooltips are wildly off because of likely typos and missing information. We really need it spelled out what applies to those tooltips on the tooltips themselves and those numbers to be checked for typos when changes are made. Of course, they need to be corrected first as soon as possible.
The actual end numbers vary much farther than intended as well for no readily apparent reason.

Can we please get these numbers fixed and some transparency on the equations that result in the final stat so we can accurately "check your work" and stop having to submit bug reports with missing or incorrect information as well as theory-craft and compare gear in game with the provided tools more accurately?