Lately, after resuming from sleep, Ubuntu requires my modem to be rebooted to restore an Ethernet or Wi-Fi connection

• I'm using Kubuntu 21.10 with kernel 5.13.0-22.
• It happens with both Ethernet, 2.4GHz Wi-Fi, and 5GHz Wi-Fi connections (two separate Wi-Fi networks).
• Things worked fine until this week.
• Rebooting the laptop does not help.
• The Windows installation on the same laptop does successfully connect.
• My Kubuntu live USB does successfully persist its connection through sleep, so it's something with my OS install.
• Rebooting the modem always lets me reconnect, but closing and re-opening the laptop lid will trigger the problem again.
• Removing the remembered connections from System Settings and re-adding them does not help.

I suspect this has something to do with DHCP business and assigned IPs, but I don't know anything about networking, so I'm not sure how to test or examine for that. I did install and then uninstall a large number of packages over the last 2 weeks, so I suspect I broke something in the process, e.g. by installing some package that replaces some built-in features, then uninstalling it without restoring the original's settings. Looking through my history, DNSmasq, Caddy, and Jellyfin-Server are the three packages that seem most obviously networking-related that got installed and removed lately.

What settings, services, potentially missing packages, etc should I look at first to help me diagnose this problem?

Solution 1:

Check these settings in Windows, as they can effect Ubuntu...

Windows

• boot into Windows
• open the Power control panel
• choose change what the power buttons do
• choose change options that are unavailable
• uncheck fast startup
• close the Power control panel
• open an administrative command prompt window
• type powercfg /h off
• type chkdsk /f c:
• approve to run chkdsk at next reboot
• reboot into Windows to let chkdsk run on drive C: