I just got the NVR32CH-4AI-S2 with that 5.xx firmware and its garbage. All HUGE fonts have to zoom out to 75% then other text is tiny. Only works with the latest DMSS in p2p. Wont work with ANY smart PSS at all. Totally useless for businesses which its designed for being a Rack Mount 4HDD NVR. Its like using a Ring or some cheap Chinese DVR. Dahua has gone 20 years backwards on this firmware.
As for your issue, are you using the latest DMSS as this 5.xx firmware seems to only work with that horrible app (all my clients use EzViewerpro).
I dont have the same NVR as you but its a 5.xx one too. In fact device discovery did not even work at all, I had to do a firmware update to get that working. Buggy and unfinished firmware. I wish I could send this back and get my clients money back. I have lots of 608-XIs in the field plus dozens more older ones with no issues.