Hi @jennaj
Thank you very much for your detailed response and information. In the meantime, I think there was another problem. It was as if my jobs were never queued, because other jobs (the same Minimap2) did not wait long to run shortly after. I have several years of experience with Galaxy and have never encountered this kind of problem, except when our local Galaxy server restarted or crashed. It seemed more like a bug caused by the large number of jobs in the queue. Anyway, my jobs are done now 
Many thanks for your help !