Just think about it. If you manage someone else's account, your device and location won't match with your client, now imagine doing actions from different locations via different devices at the same time assuming that your client is logged into his/her account too doing whatever. Of course it gets suspicious.
It is very common to have an account logged in from different locations. As a marketing agency, we handle some big accounts of celebrities and big corporations. Think about it, you think all these big companies log in just from 1 location? Hell no, they have people logged in from different locations. For example, a content creator could be in Los Angeles and the support team who replies to posts might be in Denver. It is very common in my opinion. Not saying you are wrong but we have had different experience so far.