A couple weeks ago I noticed my modem reboot in the middle of the night and assumed it was a firmware upgrade. Ever since then, my wifi devices (iPhone, iPads) will occasionally lose connection and regain it after less than 30 seconds (wifi connection symbol will disappear and reappear). This is annoying but I can live with it as it happens less than once a day (that I know of - devices may be losing/regaining connections when not actively used). However my Apple Airport Express loses connection and doesn't regain it unless the Express or modem is rebooted. The Express is ancient but has worked well for 10+ years. Wired devices (PC, Mac) are unaffected.
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If you haven't done it already, restart/reboot the modem. Pull the power, wait for 15 seconds and plug it back in again. See if that resolves the problems. If not, run a factory reset and set the modem up from scratch.
Firmware version 7.x is a new version with a new kernel. After 22.214.171.124 loaded on my 4852, the performance was pretty miserable. It took a modem restart followed by a change from Bridge mode to Gateway mode and back to Bridge mode before the modem performed as expected.