"...airgap will resolve issue."

I agree.

"high loops" are often configured improperly. My new DW with "professional" install was botched this way. Knowing what to look for, I fixed it myself. Very easy. The peak of the loop must be secured above the level of the sink-lip....right up there under the counter. However, even then, if your sink is really full the surge from opening the drain can push water over the high loop. Once that occurs, the siphoning can continue until the sink's empty. I suspect that's what happened. An air-gap installation will prevent this. That's why many people have suggested that ALL codes, not just some, should require air-gap installs.

Your dishwasher will not drain unless the drain pump is operating. Once the siphoning action began, you were doomed unless you recognized it and stopped the drain immediately.

"The peak of the loop must be secured above the level of the sink-lip....right up there under the counter."

Securing it to the bottom of the counter (and making sure it stays there) is all that is required.

While it could still cause a backup if the sink is filled to overflowing, kitchen sinks are not normally filled that high.

The important thing is to get the loop high enough that normal use of the sink never allows water higher than the loop.

"Think/hope contractor used the "loop" system....."

Maybe a little clarity about this would be helpful. Can you look at it and report? Does the existing installation have a properly configured high-loop or not?

Thank you all so much! Yes - I definitely lack clarity! I will check next weekend (in other words, will wait and have someone else check it - I am that unsure of myself) and get back to you. Thank you again.

I still have to check the loop. In the meantime, do you think it is safe to use the diswasher itself? Thank you.