Wondering if using ProtonVPN in a VPN chain is an issue.

Pretty much what the title says. I have a subscription to Proton as well as Mullvad. I’ve ordered a router and I plan on running Proton on the router and Mullvad on the device I’m using, or vice versa. I would just like to know with absolute certainty that doing this won’t somehow put my Proton account at risk, before I...