Just to be clear - you selected the "Experienced" tab and it was empty?
Yes. In story mode, I had several party tabs that were either empty, with no characters shown in the party, or that contained characters that I had deleted, so clicking on the play button would do nothing. I decided to clean it up by deleting all the party tabs. Then all my "experienced" players, under the experienced tab, except one were missing. I made a new party with the one remaining experienced character, but the next time I logged into the game it was missing too. Again, I had a party tab that showed the last missing character, but clicking on the play button would do nothing, so I deleted that tab too and started over from the beginning with a fresh party. I'll never delete the party tabs again, BIG mistake.
My experienced quest players are gone too, but they were only level 7 so I don't really mind them missing as much. However, I only deleted the parties for story mode, so not sure why my experienced quest players are missing too.
Yes, I'm still logged into the same Google Play account.