Beware! I question everything and everybody.
This is what comes to my mind as a solution to this anomaly.
Knowledge is power.
While overall Grammarly is very helpful, in some cases where we need to apply our logical sense, it shows an error. Maybe since this is a free edition, it is showing them as errors. If we purchase the original version, we may get a more detailed explanation to each of those errors.
"Life is easier when you enjoy what you do"