I don’t know
If it is a spelling error, it will underline the word in red. If it is a grammatical error, then the word will be underlined in green.
That's commonly called a bug. Even the smallest spelling error in a line of computer code can have a 'cascade' effect over the whole program.
Most likely is a grammatical error. The correct spelling does not contain the letter k at the end. The dictionary shows the correct spelling as picnic.
No, it is a mechanical error.
The red underline indicates a spelling error, and the green underline indicates a grammatical error. Note that these programs are not infallible, and it is still up to you to decide if there was really an error.
Red, however, BLUE is for potential contextual errors, i.e., "in" to "inn".
Grammatical error
grammatical error
The grammatical error in "she wanted to know why did he leave her with any reason" is "did he leave her". It should read "why he left her".
The only one who can answer this is the one who underlined the word.
Post-writing is what you do after you have all the ideas in your paper sorted out properly. The aim is to make your paper as clear and easy to read as possible, not necessarily correcting every grammatical error or spelling.
The grammatical error in "our kids know and understand what did others do three years ago" is "what did others do". It should read "what others did".