The preliminary theories (backed by the thrombocytopaenia) are that, if there’s a vaccine induced thrombosis with thrombocytopenia, it is probably immune-mediated (similar to HITT - heparin induced thrombocytopenia and thrombosis).
And then there’s some weird thing that makes them form in your venous sinus.
But there were also reports of more typical blood clots (ie DVTs), the first European Medicines Agency advisory (0) said that this was within the level of noise (im now talking AstraZeneca, so apologies for shifting vaccine as generally they should be considered separately until the evidence catches up, although everyone is quickly drawing parallels between them)
(0) https://www.ema.europa.eu/en/news/covid-19-vaccine-astrazene...
Ps apologies for not referencing around HITTs and theories around antibody-mediation for CVT. Basically it’s all pretty noisy anyway at the moment and so my here-say from the medical tea rooms is as good a gossip as any, as long as everyone is aware that no one really has any definitive idea what may be going on yet