Patch SUPEE-10752 creates the same problem (or similar) as SUPEE-10570 v1 ie the checkout breaks and doesn't redirect to payment pages, instead returns a blank page or returns to homepage, but the order is registered on the system as pending.
It seems patch SUPEE-10752 has already been released as v1 so I'm guessing the problem has been anticipated, why there hasn't been v2 released yet?
I've reverted the patch and waiting for v2 of the patch.
You can try this workaround if it works for you:
Thanks Manish but I am reluctant to modify core files by myself. I'd rather wait for the correct version of this patch by Magento devs.
That's great! no issue. Cheers