Consider re installing an earlier version of DMSS (I used apkpure.com). I recently found out that Google Store automatically updates DMSS whenever there is a new version of DMSS and people report that some of these updates screw up your system. I immediately located and then disabled the auto update item in my Google Store account. I was not aware that this auto update occurred and hate the fact that Google ticked this option without my knowledge.
By the way, from my vague memories I recall that P2P is not a secure way of accessing your NVR data so I recommend you study this issue for yourself. (The NVR manual, of course, never tells you this.) I installed OpenVPN to overcome that problem and I also ensured my NVR and cameras reside on their own dedicated network.
