https://gerrit.wikimedia.org/r/#/c/350634 wraps parser output in a new <div>. Since that patch got rolled out to the production cluster before it was reverted today, May 12, all Parsoid output in that period would likely have broken rendering and editing experience in VE. This seems to primarily affect <math> editing experience.
We need to figure out if Parsoid needs to expect this <div> as part of action=parse request it makes to the action API to process extension output or whether there are core patches that will strip / prevent this <div> before the API response goes out.
Original bug report
Since may 9 2017 the visual editor can no longer produce inline math formulas. This makes it very difficult to write scientific texts that apply formulas.