2go

Thank you @Vandrasc and @Slashee_the_Cow for your answers. I took a look at Travel settings and sure enough the value for Retraction Minimum Travel changed from 0.8mm in 5.5.0 to 5.0mm in 5.7.

Changed it back to 0.8mm, printed a few of test layers and the issue seems to be completely solved. So most likely just oozing of material during travel moves because of no retraction.
 
Before (5.0mm):
 

 
After (0.8mm):
 

 
Thanks again!