One folder not opening immediately and fields not populating

One folder of mp3 files (26) was not opening immediately, created a new folder with a different name, then it opened ok, but when i changed the name as originally and it once again took ages to open.
also the fields are not fully populating, some tracks are but most remain blank, checked in mp3tag and all ok, what could be wrong to cause this single folder to misbehave

thanks