I think it is fair to say that the UAE, nor any other country in the region, would never give its blessing to anyone coming in and carrying out the type of research that he was apparently carrying out, based on accounts from friends and academics.
From the outside looking in, it would seem that it got to the point where he simply knew too much highly sensitive information, which the UAE feared would be extremely embarrassing and potentially damaging for their own national security. I would not be surprised if he had connections in the country, due to him previously working in the UAE as a researcher in the defence sector. Every Emirati will have their own threshold of what they are comfortable to be asked and talk about concerning their own country. Perhaps one of his interviewees felt a line was crossed and subsequently voiced their concern? It was reported that many of the people he was interviewing were already known to him in a previous professional capacity.
He co-authored a paper in 2017 concerning the GCC and the Muslim Brotherhood and after reading a section, it's clear we are not dealing with an idiot here but someone who clearly had their finger on the regional geopolitical pulse. One press article I read suggested some topics that he was researching, with one being the relationship between the various Emirati tribes and recruitment into the security services. A topic that would probably send a cold sharp chill up any kandura on a hot summers day.
My guess is his early release will be announced on UAE National Day and he will be back in the UK for Christmas.