Thank you, that was useful. I think my main problem though was that I was running an older version of idtrackerai, I updated it to version 5 and it is running now.
A related question, to get data like average speed per individual in csv format (for combining with other data and analysing in different stats softwares), which method would be appropriate to use? Can the package Trajectorytools also, in addition to making lovely plots, output this summary data? Or should one calculate these things manually from the coordinates in the trajectories.csv file?