X axis sliding problem  

X axis sliding problem

Hello!

I randomly but quite frequently face a sliding on X axis on my MK3S. 😥 
I already went through the Prusa troubleshoting guide without success; from the guide I just discovered that the belt tension had increased a bit (up to 240) over time, releasing a bit the tensioning screw now it's between 264 and 270, that should be perfect.
From what I can see, guides and bearings are smooth and lubrificated (the printer is quite new).

Last time I faced the problem, I was trying to print this with white PETG, that is the material I use most of the times.
I got 3 perfect pieces, as this one: 

As you can see, this one instead suffered a visible sliding (on X axis):

Sliding is not always is the same direction, sometimes it's on the right and sometimes on the left, but happens only on X axis.

When I face the problem, I don't get any to hint on what can be the cause on this sliding on X axis, a part from this time, that I found something: there is a quite big "blob" of fused and partially burned plastic.
May it be the root cause of the problem? Or just an effect of the sliding problem?
Enlarged:

Each layer here is 0.30 mm, so the blob is quite big, 2.5/3 mm high.

I use Prusament PETG with default suggested values for its printing.
I tried experimenting a bit with some different values, e.g. slowing the speed up to 50%, but nothing changes.

Crash detection is enabled, but the printer detected it just once, and not this time.

Actually the printer is in an enclosure, with internal temperature around 22/25 °C during printing, as it's in a not warmed space, outside the enclosure the environment is at about 12°C; I got the same sliding problem also at the end of summer, with 30°C and no enclosure at all.
BTW, I don't see any sign of print deformation due to temperature change: prints are perfectly planar and regular, attached to the printing bed in any point of the first layer.

I'm not sure that such a "blob" can the be cause, as I guess that it should cause also Y axis sliding problem in the same way, but I never got it.
Do you have suggestion of what can be the cause of the sliding and how to avoid it?
Based on your experience, is there anything else that I can check that is not included in Prusa Troubleshooting guide?

They appear to be ok, but as they are not a too big investement, if it can solve the problem, I can also try changing belt, rods and linear bearings.
In this case, do you suggest me to get original pieces or do you know of any higher quality compatible items, e.g. bearings?
I ask this because I'm used to bike bearings, where cheap items (always more expensive than these linear bearings) are not reliable at all ... and I'm running out of ideas. 😉 

Thanks in advance for any help.

Riccardo