Sorry, my fault, thought it was only the AoE2DE forum. Update, I found my save games, but my progress is still reset. it happened during the Lake Poyang mission. Probably the achievements are reset as well.
It’s the MS store version, I do not use steam or any other apps next to the Xbox companion. The companion does only show the unlocked achievements, not the progress towards locked ones. (AFAIK it did not do so before either, otherwise it would indeed be reset to 0)
In Xbox Companion-console click on the game and then on tab achievements. There you can change the selection filter and also view your progress per achievement. Change the selection filter to all.