I mean, my game was among the most popular among text games until two hours ago, but now it has disappeared from all tags... I'm worried, guys. I rely on the money coming in from Itch to pay for my art assets.

Is this normal to happen?

Actually, yes, projects move up and down in search results all the time, that's how ranking works on itch.io, to give everyone a chance. Please do your own advertising and don't rely exclusively on itch.io searches.

How did you check, if your game has "disappeared" from all tags? 

While search is quite random, tags are not. There is popular, new&popular,  etc. So if you are indeed popular, and click on of the tags your game sports, you will be in the top pages for that tag.   You even have a tag that  is shared by only 100ish games. You can exhaustivly look at all games having that tag and find your game - even if you landed somehow on the bottom of that tag list.

text based has 8k games, how deep did you look? Maybe you overlooked your own game or deactivated  adult games to appear or your recent update temporarily bumped you out, while itch was rebuilding the  premade lists for people to browse.

(tl;dr your game is NOT disappear as of now)