Librtlsdr zerocopy buffers not working on Tinkerboard Armbian

I've been trying to get some RTL-SDRs to function properly on my Tinkerboard, running Armbian Bionic, Kernel 4.14y. I noticed that with the Osmocom drivers rtl_test would result in huge sample drops (millions of samples dropped each time). However, Keenerds branch did not drop any samples, nor did the presumably older Osmocom drivers from apt-get. I did a diff against Keenerds and discovered the new zerocopy buffer code in the Osmocom drivers. After commenting that out, the Osmocom drivers work fine on the Tinkerboard with Armbian and there is no sample loss. Strangely, on TinkerOS and Ubuntu OS for Tinkerboard, all of which run Kernel 4.4, I do not get sample loss with the Osmocom drivers and the zerocopy code enabled. I'm also running the Osmocom drivers on an Odroid XU4 with Ubuntu which is also running Kernel 4.14, and on Raspbian, and on those there is no sample loss. So it seems to be something specific to the Tinkerboard and Armbian with Kernel 4.14y. Not sure if the zerocopy code is just not getting activated on those other OSes or what. How do I check if the installed libusb API version is >= 0x01000105? Any ideas what could cause the zero copy code to result in the lost samples? Regards, Carl Laufer