Before the login, an anti-DDoS wait page may hold you for a few seconds to a minute depending on load. This is flood control. It rate-limits bots so they cannot hammer the login behind it, which is part of what keeps the market reachable under pressure.
It is mildly annoying the first time and normal by the third. If it stalls for much longer than a minute, the cause is usually your Tor circuit. Build a fresh circuit and retry, or switch to another address in the pool.
When the queue clears, the captcha renders and you can log in.