Hi @Laura_Thipphawong, welcome to the Asana Forum!
This could be related to how your colleague is sorting projects in the sidebar, at the moment, you can sort by alphabetical, recent and top. Please note we currently show a certain amount of project, if the project they are looking for is not listed there, they should select Show more.
If the issue persists, I recommend you to contact our support team and share the URL of the project they should see in the sidebar, this will help us investigate further: How to contact our Support Team ✉
I hope this helps! Let me know if you have any other questions.