I have had the same issue and used the same workaround.
Just try another exit or simply use something else
Would be nice if the site told me my exit IP is blocked instead of tricking me into filling a thousand captchas.
To begin with I don't think blocking TOR exit nodes for spam makes sense. They should be exempt.
You could stop them spamming by making their browsers do some sort of proof of work pr. login/captcha attempt.
Verifying proof of work can be done instantly, but would bog down a spammer.
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