Сброс локальньіх сохранений в случае критической ошибки происходит, чтоб игра не оказалась полностью "запоротой". А вот почему на сервере не сохранился прогрес єто уже другой вопрос... Интернет я так понимаю не пропадал? О каком именно прогрессе идет речь? Просто действия на уровне, или несколько пройденьіх клеток на карте мира? Как много?

I don't know if this is exactly what has been reported, but I just had a roll back of a few levels, I completed them with pick axes and they are back to before I completed them, it could be just an inconvenience if really the server was back like 10 minutes ago but the big problem is: the tools I used to complete those levels are not back in my inventory (including one big hammer, ouch) ! And just in case, refreshing the page doesn't help.

Try to delete all browser cache/cookies or start the game in anonymous tab, login from it and see if that items return. The items should not disappear on the server, but there may be a problem of corrupt/inconsistent local data.

All progress including completed levels, purchased items, spent items are tracked on server and should not be lost. Everything you do int the browser is repeated and validated on server, thus if you play some level, spend items or earn some loot, it's all done on the server in one transaction. However, it is possible that client side in the browser may produce partial updates due to bugs. That data is stored in browser's IndexedDB - you can wipe it via browser developer tools, by clearing cache, or when you open the game in private tab - it clears all page data for the length of that private session. If the problem persists in private window/tab, then it is something on the server.

Rollback happens when client sends your actions in the game and server is unable to reproduce your actions to get desired results (complete the level). This is often happens when I have uploaded the new version of the game with slightly changed game mechanics or level generation which resulted in slightly (or completely) different level, different token colors, which in turn make your swaps not producing matches and level not beaten with your actions. In that case server issues "desync" command and client wipes current state and reads new state from server. If map is reverted back, but you are certain that items were not reverted, then perhaps there is a problem in "wipe/revert" on client which needs to be investigated.

No, this is not a solution to the problem

Just today had the same bug. Rollback for levels but gears I used for them are not given back.

Try to open the game in anonymous browser tab or from different device where you did not play the game and see if from anonymous tab number of gears is correct.

Indeed, there was a server bug which caused only activation item to be returned (pickaxe, spade), but not boosters used inside level (gears, hammers, etc). Fixed now.