Carl's game overhaul mod, public release, now includes all of his Dine Out fixes and one of the things it does is actually tell you when slots on tables are blocked causing failure to be able to deliver food. It gives this message for any tables that visitors are at, even unplayed sims at the restaurant. And it kick starts chef's so they don't need to be reset to get them into the kitchen.
Bienchen also has several restaurant mods which fix all the various issues, including a new one that kick starts the chefs as well.
So if you are willing to use mods, either of those modders has the solutions. Bienchen's are modular (you would just use the ones that you want) while Carl's is a all-in-one solution that also does other things as well. Pick your poison.
I just finished 2 sim weeks where I had my played sims eat every single meal at restaurants because I was testing out how Bienchen's new mod works and I can say that my restaurants worked 100% of the time, with not a single issue, for that entire 2 sim weeks. My sims were in and out, fully fed, in under 2 sim hours even (except when I had them hang around for Karaoke in my restaurants that offer that). It was glorious.