I'm a plumbing contractor and my customer called to say her drain standpipe had started to foam out of the top near the very end of the drain cycle, allowing time for the suds to build up I guess.She has been doing the SAME thing for over six months and this foaming just started a couple weeks ago. It could be a main drain issue, blocked somewhere downstream maybe causing it, or perhaps the detergent has changed somehow.
HE detergents create very, very little foam. She may have switched detergent brands. Or there was a load done with a soapy car wash rag or something similar in it.
Washing machine bubble overflow can be encountered from a few different problems. A partially clogged drain or a dirty catch screen on the discharge line is a probable cause with those symptoms. If they're truly doing the SAME thing, and no I forgot to mention's come up, what else could it be but a clogged line? More often with the bubbles everywhere problem it is user error in how much or too little detergent is used or excessive bleach, in conjunction with load size.
Hire a new plumber! :) Are the bubbles coming out of the washer, or are they coming out of the drain? Hook your washer drain hose to the side of a 5 gallon bucket to determine the source of the bubbles. If they exit your washing machine as bubbles, adjust your detergent. If they are not leaving your washer as bubbles, check your plumbing. Do you live in a multi story building with your washer on one of your upper floors, then check for proper venting from lower floors.