Has anyone had this problem with Railzip?

Hi all,
I recently used Railzip for the first time.
I dutifully followed the instructions on the bottle ie applied Railzip
with a cloth, left it for 12 hours and then rubbed the rails with a
cloth.
I tested all my 0-6-0 tanks engines and a Class 08 shunter and their
performance has improved beyond measure.
However, my Class 37, Black 5 and 2-6-0 now all suffer from poor
traction. Anything more than a carriage really makes them struggle.
I've tried to clean the wheels of all three and the performance of the
Class 37 improved but it's still nowhere near it's previous
performance.
Any idea's on what I can do for my tender engines?
Regards.