“At start /jp, /jn, /jo, /js, /jc queries are requested separately, then /ja is requested in every 5 secs.
Does it have some practical sense?” –> this is for backward compatibility: not all hardware supports the /ja command, due to the limit of the microcontroller capability. For that reason, it needs to check whether /ja is supported or not, if not, it needs to send separate queries.