It is called "siphoning" - several discussions here about it you can browse - and has several possible causes. Most common is pressure fluctuations during processing from heat adjustments. Since you are getting used to new equipment and stove that is likely. Other causes are ring bands, over-packed food, air bubbles, etc. All need to be eliminated for the best seals to develop as siphoning deposits foods on the jar rim so can lead to seal failure.

http://nchfp.uga.edu/how/general/cannedfoodproblems.html

Dave