Jamesc Your choice of the farmlands glycerine may be the reason for your losses, the glycerine they sell now is very thin compared to the shine glycerine they used to sell.
I used to get my glyc from farmlands , but when they changed supplier the new product was a lot thinner and that puts the final solution out of kilter ( the solution leaches out of the strips)
I now purchase my glycerine direct from bell booth in Palmerston North 200l at a time Shine USP/BP grade , also if you used the ovaboard product, that could also be problematic as
that stuff is made from recycled board and so could have anything in it. I would suggest that you find a supplier of what used to be called food grade fiber board but now called food contact board , this can be obtained here in the Waikato at Attwoods in hamilton and they will get it cut to size .If there is an Attwoods down there in CHCH they may be worth a visit
Check their website under greyboard I think.