I was switching to Spectrum Fiber from DSL and had an odd problem.
The P2P would go online on my NV4108E, but only for 24 hours. Sometime between Midnight and 6AM the P2P would go offline, and no rebooting would fix it. Oddly though, changing the LAN (yes, LAN not WAN) IP address of the NVR would bring it back online until the next evening.
Initially I thought the Invincible router was the culprit, so Spectrum replaced it with another one, but there was no change. Switching to the Non-Invincible router had the same issue. I then switched to a TP Link router and even put the NVR in the DMZ zone to bypass the firewall, with the same results. Replacing the Fiber modem changed nothing. Switching back to the DSL internet allowed it to work perfectly.
Spectrum swore they do not disable any devices on their network, but this was to consistent. NVR port forwarding would also be disabled, even if it had never been used. No combination of P2P and port forwarding would work, even if neither of them had been used.
I know a little something about networks, so I purchased a "Privacy Hero II" router, which has the ability to encrypt all the traffic, and put it in between my TP Link router and the NVR. Magically the P2P of the NVR stayed online.
At this point I was in contact with Spectrum Corporate who assured me there was nothing they were doing to disable the P2P on the NVR. I proved to them they were doing just that. They have continued to work with me, even months later saying they cannot figure out where this is being done on their network. Even comparing it to another Spectrum site I have with a very similar setup that worked perfectly.
I bought my Privacy Hero II routers with NordVPN preinstalled on them, but the P2P funtioned without utilizing NordVPN. This router can encrypt traffic without NordVPN, but NordLynx has the ability to run much fast than a standard VPN.
I also had another location with Spectrum Cable (Not fiber) that had been up and running for years with a Spectrum modem and a 3rd party router. I upgraded the Spectrum Cable to a Gigabit connection, but was having a problem with my 3rd party router rebooting. It was not designed for gigabyte traffic, so I believe it was being overwhelmed. I switched to a Spectrum Invincible router and ended up in the same situation, where the P2P of my Amcrest DVR (an AMDV10818) would get disabled sometime between midnight and 6AM everyday. I had already purchased a 2nd Privacy Hero II for this location, but had not yet installed it. Installing the DVR behind the Privacy Hero II allowed the P2P to function.
Note that the Privacy Hero II does not support port forwarding, so here is a work around: Cascade the Privacy Hero II to the 1st router on the network and open a WAN port on the 1st router. The IP cameras are on the same network as the NVR, behind the Privacy Hero II. I have the WiFi of one camera attached to the 1st router, which is ported to the WAN. This way I can access the camera via port forwarding and P2P on the NVR. Note this only worked with the ethernet attached to the 1st router and WiFi attached to the Privacy Hero II, and I can't explain why, but I went with it.
Pretty weird eh?