This problem has been persistent for a while, just happens every so often at random times, nothing changing. I also do not know how to reproduce the problem, but I\'ll give a de
I tried adding :
if(ISERROR(importrange...
and it works.
It doesn't mean the error disappears, but when it happens, you just need to reload the sheet and wait for while and let it update itself.
It is much more practical than manually changing the big letter to small letter.