Toilet Problem

[kohringmw]

I have two toilets on the second floor of my home. Yesterday, the toilet in the master bathroom would flush but the tank would not refill until I flushed the second toilet in the other upstairs bathroom. I tried this several times with the same result. I suspect a vacuum break problem somewhere. Please advise. Thanks.

[DIY Guy]

Are these toilets back to back on a common wall?

Do you have water in the sink in the problem bathroom?

Can you make the toilet refill by turning on the sink?