I’ve seen this a couple of times before. In both cases it was caused by buildup of paraffin based emollient creams – the treatment used by some people with skin conditions. Notorious for causing severe burns due to build up on bedding and nightware, I wonder if this stuff is also a contributory factor in some dryer fires.
Agree, seen it several times and even posted pictures several years ago.. One was in a beauty salon so I’m guessing it was some chemicals they used. Another was a chap who used creams for muscle strains etc.