Compilation mode next error isn't searching all buffers

Compilation mode next error isn't searching all buffers

[Eric Chun via Users list for the GNU Emacs text editor]

I see the following at Compilation Mode (GNU Emacs Manual):"If the current buffer contains error messages or matches, these commands will iterate through them; otherwise, Emacs looks for a buffer containing error messages or matches amongst the windows of the selected frame (if the variable next-error-find-buffer-function is customized to the value next-error-buffer-on-selected-frame), then for a buffer used previously by next-error or previous-error, and finally all other buffers."

This seems to indicate that next-error function should switch to other buffers if there are no other errors in current buffer, but that doesn't seem to happen.
Here are the steps I followed:* First, I open an org file in Emacs.* I then create a sparse tree using a regular expression.* I then type M-g M-n to move to the next occurrence of my search string but it doesn't work.  I get a message saying "user-error: Moved past last grep hit".* I kill the pre-existing "*grep*" buffer in Emacs.* I then try M-g M-n again and it works.
Why doesn't next-error function jump to the next occurrence of search string found in current buffer?  It seems to still be looking for occurrences in the grep buffer.
I'm using Emacs 28.2 on CentOS7.