Nitter gets overloaded and sometimes blocked. Consider as an alternative an addon [1] that utilizes multiple Nitter proxies and has a UI tool to test latency to each one. I would expect them to especially be overloaded right now with the current events going on at Twitter.
Yes, I mean that's one of the things you probably want to turn on anyway for a useful experience (if you curate the instance list as like all things like this there are fly by instances that either disappear or start serving up malware) - but really your own instance is probably better, non public and known quantity
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[ 6.9 ms ] story [ 19.8 ms ] thread[1] - https://addons.mozilla.org/en-US/firefox/addon/libredirect/
Also libredirect is pretty good (does more than just Twitter)
LibRedirect won't help in this case, unless you enable the option "Auto-redirect offline instances to online ones" which is turned off by default.