I understand that you recently added a new staff member to your store and post this you have noticed that every so often you are unable to perform basic actions that you, as the store owner, should be able to perform, is that correct?
You have also found that your colleague, the new staff member in question, can then perform these actions that you should be able to perform.
What I suspect might have happened is that you may have added the Staff member and perhaps accidentally transferred ownership to them. Or, it is also possible that they use the same machine to log in and there are some conflicts there.
However, if you can tell me the process you took to add this new staff member that would help a lot. Additionally, if you could check on your staff permissions page to confirm who is the current owner that would also help a lot here. You can follow the guide here to find out how permissions and managing staff can be accessed.