Valve announced yesterday that it has been forced to take steps to manage the bandwidth as a result of increased traffic due to COVID 19. It is, therefore, scaling back auto-updates to "spread out" the load on their servers, which is Valve talk for disabling it. This means that only very recent games, played within the last three days will update by itself, anything else you will have to update manually like some caveman, as other updates will be done over the course of several days instead of immediate.
Valve is very direct about the fact that even they are facing high loads on their servers in these times, and that this is for the greater good.