'In linguistics, grammar refers to the logical and structural rules that govern the composition of sentences, phrases, and words in any given natural language.' - wikipedia (writer Hannes Hirzel is listed as the oldest writer for the Grammar entry on wikipedia... an entry with many many many hundreds of revisions).
So why "grandma errors" and not grammar problems?
Firstly grandma is a word spelt correctly... however used in that context is incorrect. It is a grammar problem itself.
It also sounds like grammar. So it's a self describing word illustrating itself with a meaning completely different to what it is supposed to be used for.
I use "grandma errors", rather than "grandma problems"... because "grandma problems" is used more often when people discuss problems with their grandmas. If someone says they have grandma errors.... and are talking about their mums mum, then they are some sort of star trek nerd that has one room in their house devoted to star trek collectibles, or perhaps a robot.
So have you checked your writing for splling and grandma errors?