Its the rustins stuff. I don't remember any problems with the previous cans. Infact I have some left in a small can, I might try and see if any different. Ive bought exactly the same product down to the barcode being the same.
I wonder if the weather as well isn't helping things too, but suspect not.
The varnish is this stuff:
https://www.uktoolcentre.co.uk/produ...iABEgK0S_D_BwE
Though not from that retailer, and infact I think it was a different retailer to the first can...