While working on a drawings, material tags literally started to disappear from the drawing. Switched to another sheet and all tags were gone. Tags still appear on the another sheet but can't get them to recognize the material on the first first. I have shut down, rebooted, reloaded tags, turned off all worksets, turned on all work sets, checked visibility graphics, etc. ...I'm pooped...can't think of anything else to try..any suggstions