How long were the exposures? With a 760nm filter, they would need to be very long indeed.

I also use a 720nm filter (R72) but with Efke IR820. I shoot that at EI1, i.e. f/16 for 1s in full sun. Rollei 400 would probably work at about EI4 with an R72 (1/4s f/16 full sun).