I had a lot of trouble with this last batch of a 25kg bag of Veloria Schooner. The BH efficiency dropped from 63% to 52%, which was driving me mad. So, thankfully, this is the last brew with that bag what is left is pigeon tucker.
I think it may have something to do with the humidity when I bought it, the humidity lasted a week or more. Even so it shouldn't have made a 10% point difference.
Brewing a Burton Bridge Bitter clone from Wheelers book used to enjoy this a few years ago but with more experience it could come out a lot better.
Dough in and after a few minutes of stirring, left the Guten to carry on with the mash @ 67C with the return valve fully open.
Temperature consistent top and bottom throughout the mash. Iodine test shows good conversion.
In with the speciality malts, in this case light crystal and Carapils.
Hoist out the grain basket and give the mashed grain a good squeeze. Vorlouf until running clear
1,046 was the target with temperature adjustment weighed in @ 1,048. Nicely clear into the fermenter.