Wet QX and bees stuck would indicate that bees had vomited stomach contents. Must have been trapped in some way and vomited due to heat stress. It would only take one layer of bees disabled on queen excluder to prevent ventilation leading to them all smothering.
Design of CDB hive was ideally suited for wet maritime climate and prevented ingress of water in winter. Traditionally the section crate for this design was only three sections wide and a stack of crates took advantage of the "chimney" affect of rising heat from the centre of the brood box...
Appear to be very old bees who have lost their hair. Very often seen where a colony has been queenless for a very long time and workers, having no brood to rear or much work to do, survive for long time.
Google "Irish Bee Supplies" - they have two gas operated vaporisers advertised in "hygiene/disease" heading . I have no connection with supplier and I have had no experience of using either item, but have heard positive reports.