Is it possible that you set a short DHCP lease ?
Also is there a limit on the VPN that you are using, some free ones disconnect regularly.
Are you able to access logs to confirm whether the dropouts are after an exact period of time?
Assuming you have done a factory reset so that all settings are reset then started over then there are other options to try…
When I want to determine if there is a hardware problem I use 3rd party firmware such as DD-WRT or OpenWrt, I would also not use the VPN until I had confirmed or eliminated the hardware as the cause of the fault.
This is the OpenWrt page for your router, even if you do not install it you can learn a lot about your router.
Usually installing means downloading three files
1. OpenWrt Factory (first stage of iIstall)
2. OpenWrt SysUpgrade (Last stage on Install)
3. A copy of the Linksys firmware (in case you want to restore it)
Out of interest, what Country are you in?
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