Only 1 out of 7 successfully created section listed in result of List course sections request (api/v1/courses/SECTION_ID/sections/), however i can see them when calling them explicitly (api/v1/courses/348153/sections/ SECTION_ID)
It looks like there is a limit (10 in my case) on number of returning section. I did some test with postman: there were 9 existing sections prior to creation of new one. Then I created another one, it did showed up in result of List course sections request. Then added one more, as result of the create request I got my new section back. However when i run List course sections again i can see only latest(second one) section being returned among with 9 original ones. When I delete second one, then first one is being return among with other 9.