Version 5.0 issue

After upgrading to version 5 I suddenly get a browser dialog box saying Floatbox does not support quirks mode
Page need to have a valid doctype declaration.

I know Floatbox https://floatboxjs.com/ is not part of Stop Spammers plugin but something in version 5.0 seems to have a bad effect on this. Downgrading to 4.3 makes the problem go away.

Any chance of a fix?

https://www.ads-software.com/plugins/stop-spammer-registrations-plugin/