Lightsail instance not connecting with one of my ISP through RDP or http?

Based on your description, it sounds like you're experiencing a connectivity issue specific to your primary ISP when trying to access your Lightsail instance, while other internet connections work fine.

Since you mentioned the ISP has a new IP address pool and your IP has been "whitelisted," I'd recommend checking the following:

1. Verify your Lightsail instance's IPv4 firewall settings to ensure they properly allow traffic from your new ISP IP address (163.227.213.56) on the necessary ports:

• RDP (TCP port 3389) for remote desktop access
• HTTP (TCP port 80) and HTTPS (TCP port 443) for web access
• SSH (TCP port 22) for troubleshooting

2. Test basic network connectivity from your office to the Lightsail instance using tools like telnet or ping to check if there's any fundamental connection issue.

3. Check if your new ISP might be blocking outbound connections to certain ports that you need for RDP or HTTP access. Some ISPs implement restrictive firewall policies.

4. Ensure you don't have multiple RDP sessions attempting to connect simultaneously, as Windows Administrator accounts typically only support one RDP connection at a time.

5. Verify that your instance's status checks are passing and that it's not experiencing high CPU utilization or other performance issues.

If these steps don't resolve the issue, you might need to contact your ISP to check if they're blocking outbound connections to AWS IP ranges or implementing any network policies that could affect your connectivity.
Sources
Why can't I connect lightsail's website by using public ip | AWS re:Post
CAN'T CONNECT TO AMAZON LIGHTSAIL | AWS re:Post

issue seems specific to your primary office ISP, as the Lightsail instance works with other networks (home, LTE, backup). Since the ISP recently updated their IP range and you’ve 163.227.213.56, you can try:

1. Ensure** ports 3389 (RDP), 80 (HTTP), 443 (HTTPS), and 22 (SSH) are allowed for your ISP IP**.
2. Some ISPs block outbound RDP (port 3389) or AWS IP ranges. Confirm with your provider.
3. Make sure the instance is running properly with no high CPU or session issues.
4. Check for any egress rules blocking AWS. also, try bypassing the router if possible.
5. For temporary workaround, Use a VPN or set up Remote Desktop Gateway to tunnel over port 443.