There were two issues associated with connecting and ANAN radio running with either Thetis or PowerSDR software using VAC to a VARA modem.
One was a very isolated corner case when SNRs are high which enable high VARA speeds and VARA enters an IDLE state where neither station is transmitting. With high speeds and in the IDLE state, ANAN VAC timing would cause the connection to drop after one minute. Special thanks to Jose for posting an update to VARA on his website that addresses this issue. This new VARA update does not change the version number. You just need to copy this new version of VARA.exe into your VARA folder.
The second issue is more complex. I won't try to rehash it here. Check this Apache Labs ANAN forum thread for more info. Be prepared to have your eyes glaze over.
With both forward error correction and ARQ, the VARA modem is very robust and handles errors caused by digital audio sample rate differences between the radio and computer. I just turn off the resampler without any degradation to packet error rate or bit rate for small chat messages and larger file transfers.