Is this, by any chance, originated from the sub called ignore? In that case is probably my bad because is set as the image of the channel. (I was playing with lemmy in the previous version and forgot about it, sorry. It will not work since your browser can't access local file that easily without breaking the sandbox :))
Edit: I removed it so you shouldn't see the alert anymore. What I wasn't expecting is that apparently every sub is loaded even if you don't visit it.
Because I wanted to try if others URI schemas were supported instead of http / https. file:// was a valid one. Don't worry, the day an attempt of data exfil will happen, you will not see it though your console logs.