Blocked Requests (406) Based on Firewall Rule Cached

I have the country Russian Federation blocked in the firewall and I suspect these requests are being cached by Cloudflare. Google PageSpeed Insights tells me it cannot test due to a 406 error. Clearing the Cloudflare cache resolves the issue immediately.

Is it reasonable that this may be happening, and if so, is there a workaround to avoid issues with Google?

You can try:

You can go to Security Events to see which rules/rulesets were triggered, as well as the details under Activity Log. After that, you can create a Skip rules to avoid blocking.

Regarding 406 error, you can take a look at 4xx Client Error ยท Cloudflare Support docs.