Did you try to open the problematic website using Opera Mobile instead of stock Maemo's browser? I'm not sure if the HideUserAgent affects also Opera's User Agent. Captcha in the search view on TMO also works using the Opera Mobile.
If it helps, I get an error from slashdot (uses letsencrypt) about no common ciphers. All I do is press enter again on address bar and second time it loads.