Hi!
I have some random irregularities on my layers and I cannot find the solution. Im printing with 185º PLA but sometimes it happens with ABS. This issue could appear on the first layer, in the middle or in the top and not necessary in the whole layer.
Always on diagonal prints?
My guess is that too much resistants/too little power make a motor skip micro steps. Could also be vibrations in the bed or hot end but you should be able to see and/or hear that.