Save my sanity

[curious aardvark]

one scenario.

bear in mind that the x gantry is pretty much always going to be slightly higher on the side with the screw and motor than on the side that just has wheels (it's one reason to always buy an i3 with dual z-axis motors).

So that accounts for the 2 left corners (as you look at the front) being level.
Also bear in mind that the print bed is solely supported by 4 wheels running on a piece of aluminium extrusion. So that odds of that ever being perfectly level at all points during it's travel are fairly small.
If the rails is slightly off - in any direction or axis - then the bed will always change it's 'levelness' during movement.

I can see several circumstances where the nozzles is higher in the middle.
With a print bed with side support bearings and rails - you can pretty much guarentee once levelled it'll stay levelled.
With a few wheels and a single central support - it could tip to either side or hit an irregulariy in the extrusion.

I mean we're talking tenths of a millimetre here - so you're not going to look at it and think - ah ha ! it's tilting to one side.

But because creality insist on making these peices of junk, the people who buy them are saddled with a lot of unnecessary problems and issues.

Given that you have added glass - the odds are that the prinbed is flat, so you need to look at the x gantry and bed support rail.
There are probably mods and guides you can make and follow to get the bloody things as level as possible.

But the inherent design is always going to be against you :-(

First thing to check is that all the wheels are as tight to the extrusion as they can be made. That goes for the print bed wheels and the z-axis wheels.
If that makes no difference see if there's any way the bed support rail might not be perfectly level.

And look around for mods to improve both.

Good luck !