Wouldn't you know it! I have run the washer twice now and the problem isn't again happening. The house where it is located is my summer house so the washer is not used often. That, together with its 50 plus year age could somewhat explain. Still, it is highly likely the problem will again happen. So we'll have to wait until then to diagnose as per your excellent reply!

Possibly related to enzymes in the detergent, as discussed in several of the posts in this thread. Tide Free and Gentle does contain enzymes. The "Free and Gentle" part relates to it having no dyes or perfumes. Perhaps items are getting slightly damaged by that hole in your dryer drum and the enzymes are further deteriorating the damaged fibers.