It can’t be filament or a clog. The length of each diagonal extrusion path changes, so it is impossible for that to align perfectly with a pattern on the build plate like this.

It could be contamination of the build plate, or an issue with sensor noise related to however the the bu checks for bed height. Depending on method of bed height sensing, it could also be related to bed leveling versus the sensor mapping resolution. Again, this is just a general hardware assessment. I don’t know the specifics of how this machine works and have no interest in learning anything about it. Hardware wise these are the issues I can think of. It also looks like a high first layer to me, with an additional issue too.