Getting kicked out of 1-2-1 Zoom meetings regularly on a free account - WHY???

I have a free account and only ever have one other participant in my meetings which are 50 minutes long.  For the past two weeks I have been getting kicked out of Zoom regularly after 40 minutes despite signing out and in again under my Zoom login details (advice from one Zoom website entry) and ending my meetings completely and restarting them (as advised above).  My understanding - and the latest on the website, dated I think 29 April - is that 1-2-1 meetings with only two participants are unlimited.  Why is this happening and how can I stop it?  It is infuriating and makes me look hopelessly unprofessional.  Please, please can one of you techies out there give me the correct advice let me know how to correct this!  Thanks.