I am not a plumber.....FWIW
I have had the same issue and learned that it was a "low flow" of water coming in to the toilet tank. Same issue happened with my dish washer (not my wife, the actual machine that washes dishes)
In my case it was a metal ballcock valve.The new ones are plastic and I believe they are part of the "toilet repair kit". It is not a difficult part to replace if you are comfortable with DYI.
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