I deploy ISR 4331 Routers with a SM-X-ES3-24-P installed (EOL, I know, we're working to move to a new module eventually) to multiple offsite platforms that all have identical (minus IPs and names) configurations. Lately, I've had two separate platforms report that the enabled SVI has, essentially, stopped being enabled.
When building and configuring the routers, we follow the Cisco directions of how to enable SVI:
ethernet-internal subslot 1/0 platform switchport svi
Then wr mem, reload, confirm that it's still there, then load our start-up configuration (that also has that line in it), reload, and confirm everything is still happy. It's been working great for over a year across 15+ different platforms that have 3 ISR 4331s on them.
I have done testing in my lab, and the only ways that I have found to remove the 'platform switchport svi' line is to either 'no' the line out, wr mem, reload, load a new startup without the line as well; or to use a new 4331 that hasn't had it enabled yet. The personnel out at the platforms have reported that they have not disabled SVI, nor do they have any idea how to, and have not replaced the equipment.
But 2 separate times, at 2 separate platforms, they reported (with our guidance of what to look for) that 'platform switchport svi' is not in the running configuration, and reloading the router does not resolve the issue.
Does anyone know of any OTHER way, or situation, that could cause 'platform switchport svi' to be removed. For FYI, we're running IOS XE 16.12.05 (Gibraltar)
Things I've tried to brick a 4331 with: 1) Removing SM-X-ES3-24-P before/during/after turning on ISR 4331. As soon as I plug the SM-X-ES3-24-P back into the 4331, SVI comes right back to the running-config. 2) conf t, no platform switchport svi, copy run start, reload. Once it comes back up, SVI is still enabled. Unless I wr mem, the SVI change won't stay persistent. 3) Installing a different SM-X-ES3-24-P after SVIs have been enabled already. No change.
I cannot share running configs. Any help or troubleshooting ideas would be appreciated.