Looks fine. Comes out one single strands no bubbles nice and solid.
+John doe yes they do stretch a little, that’s why I have the belt tensioner on the y axis and every once in a while ill re tighten the x axis belt.
I don’t know how to add people’s names to post yet so forgive me if it doesn’t work
T5 and T2.5 belts are prone to stretching, especially around small gears like you have on your steppers. To test if this is the problem, use an off-cut piece of belt (eg: about 5cm long) and put it along various sections of the belt, teeth to teeth (particularly where the teeth on each belt are when the hot end is in the middle of the machine. The teeth should fit perfectly in the gaps of the other belt. If they don’t and “get out of sync” then your belt has stretched and needs replacing.
This doesn’t explain the problems with the Z (unless you have one Z motor and a belt between them, like the old Sells Mendel did). I would check that your 10x10x10 test box is actually 10mm high.
Also check that your X carriage is square to the Z smooth rods - otherwise it won’t move properly, which I’ve seen cause weird issues with Z moves (where they seem to lose steps).
Note: I don’t see anywhere near as many problems with GT2 belts and pulleys. The minimum bending radius for GT2 is much smaller, so they last a lot longer.
PS: Changes in room temp affect a lot of things on your printer, including just how much heat your stepper drivers can get rid of. Even 1-2 degrees can make a difference.
Maybe just your nozzle jammed? I heard about people finding a tiny stone in their nozzle after using a certain fillament.
Anyway, the hobbed bold eating away the fillament should tell you enough. Fillament can’t get through…