I am logging into nvr directly with IE. But to log into cameras I only use IE.
I have had the other system in place working damn good for over 3 years with 16 cameras.
Stick an SD card in one of the problematic cameras. First, the camera will record a trigger box on a subject and viewing this raw footage may help figure out why your triggers aren't working as expected. Second, it will let you know if the issues are with the raw camera recordings, or something with the NVR system. You'll still record everything to the NVR, you can just have the SD recordings to compare the two.
Got home about 45 minute ago and pulled nvr. Reseated hard drives and board connections. It seems to be working as should except renaming cameras on boot up.
I hope it was that easy and it stays stable.