Assuming you handled the pagination correctly (as others noted default number of location returned per request is 10 with maximum been 100), I would recommend you:
Check in GMB that location is listed under the account/location group - if it is not there you won't get it through API since you don't manage/own it. As long as you manage/own it you should be able to list it despite its status.
If it is listed but you still are not getting it - write ticket to Google support at https://support.google.com/business/contact/api_default and they should fix the issue (happened 2-3 times to me)