Bug of unknown cause removes ticks and makes saving impossible

The attached world has, for some reason, has no ticks (you can easily check by igniting tnt) and can't be saved. I don't run into this issue with other worlds, maybe because I haven't dragged them trough almost every snapshot since 1.13.

As this is a potentially harmful bug capable of destroying worlds it should be fixed as soon as possible.

 
(World is too big for Jira, so here's a Drive link)