I believe the issue is that there is a very limited number of public spaces so its elbows out in the scramble for all who want to be there to get them, then things have a way of going wrong so that official observers are, quite accdidentally, shut out from observing. In some countries suddenly a number of off duty policemen decide they want to have those seats for themselves and arrest anyone who doesn't back down when barged out of the way. Of corse it needn't be people as reputable as policemen for it to be organised to occurr that way.
In any case the idea is that Justice must not only be done it must be seen to be done. Telling amnesty they are nobodies in the eyes of the courts is not really supporting that.
According to the quote in the tweet itself the proceedings are accessible to them and all other members of the media over a live link.
Amnesty really needs to explain why this is not adequate, and if it genuinely is not adequate why the deserve this special access over and above any other party with a strong interest in reporting this case.
As already being mentioned by someone else, the live link breaking down (coincidental or not) or being intentionally muted by the court (for whatever reason), could seriously obstruct the assessment of a fair trial. Spoiler alert: it already isn't, even if only for the judge's bias, so one might even argue that AI doesn't need to be there to re-establish an already given.
However, more crucial here is that AI does not have any official monitoring status. Sure, they have good reputation, but ultimately are "just" an NGO. It might have been a different story if this was an official (UN) body safeguarding fair trials. But I'm not even sure if those exist, given that courts are often considered an "internal affair" of a country. If there's something wrong with them, the official way is usually to proceed to an international court, after having exhausted your options in a national court.
Also, AI itself is not without controversy. It certainly does a lot of good work, with most people involved having nothing but good intentions. That said, I have personally witnessed how the organization (at least once) made some seriously politically damaging statements for a ruling government, but as it later turned out based on false information. That itself can happen. But when AI was privately informed (with evidence countering their statements), about how they were used for a political agenda, they still held on to their initial stance. That was rather surprising and even shocking to me, for an organization like AI. Only years later, did I finally hear about questionable personal relationships between the local political opposition and AI staff. From what I've heard since, that was neither the first time that AI wasn't as politically (or nationally) neutral as often thought/claimed.
I doubt that the above has much relevance in this particular case though. Still, apparently AI isn't always above using information "tactically" for their own and/or political means/ends.
Over the course of these hearings, the "live link" has had a habit of breaking up or otherwise become unavailable at short notice, as Craig Murray has reported.
This might be entirely coincidental, but regardless, I can see why observers would find it not adequate.
I'm sure that's annoying, but given the nature of what is being discussed it's hard to come up with a scenario where that has a serious impact on the observation of justice. Not least because if the live feed goes down at the same time as something bad happens that would give an enormous amount of ammunition to Assange's defence team.
“Something bad” in this context is stuff like the judge reading pre-written decisions rather than elaborating them on the spot. Without independent observers, there is no “ammunition” to be had, because it’s simply one’s word vs the authorities’.
As someone else mentioned, this is the sort of thing that, when it happens in “bad” countries, we often call with certain choice words.
The audio quality of the medialink has been reported to be so poor quality that for long stretches nothing but static is sent out. There is a limit on how much independent observation that amnesty can do in such conditions, and it gives a massive loophole for other regimes if amnesty would tolerate it.
A public hearing having (excluding a few for the family of the accused) no seats in the court room for the actual public is not a public hearing, but a secret one.
In any case the idea is that Justice must not only be done it must be seen to be done. Telling amnesty they are nobodies in the eyes of the courts is not really supporting that.