Help me understand this please.

I hope someone here can help me understand this because everyone is have talked to cant give me an answer.

I run a home server that hosts some services and use a reverse proxy (NPM) with Cloudflare. I have used this setup for 7 or 8 years, and I recently was helping a friend setup his home server but his big problem was that his ISP changes his external IP address every few days.

That got me thinking I have never updated my IP Address with cloudflare. I investigated and relealized I have had the same external IP for 7 or 8 years.

I have spoken to my ISP and they said their IP address renew everytime the modem restarts but in my case this has not been happening. I have gone through 3 different modems in this time, CODA-4582, xb7, and xb8. I tried to keep the CODA modem for a long as I could because I had a unlocked speed profile so I was pulling 5GB/s when testing with speedtest.net or fast.com or even downloading from steam. When I switched to the xb7 the speed returned to normal but my external IP did not change.

Recently I have noticed my XB8 modem has a different WAN ip listed in the logs, but the other IP address still works when accessing my home server or when I go to a whats my ip website.

I have also spoken to a colleague who is a Network Headend system administrator and he also told me that this should not be happening.

Has anyone ever had this before, im just wondering if something is wrong or is this just how it is?

I have Dynamic Residential Internet. I do not pay for a static IP. Cloudflare is used for DNS for my domain. I dont use Cloudflare Tunnel I do not have anything setup for a DDNS

Edit: added more info