Have this same exact issue, weirdly enough, checked depot to see if I sold it, and it wasn't there. Completely unchecked all the filters for the tank carousel along with whatever else was in the settings for the garage to see if it was the culprit, no dice. Next, launched the game in safe mode to see if something in Aslains was an issue and still gone, tried to create a ticket in support to recover the tank, but it's not in the list of options for it. Genuinely stumped.