Hi Tia,
It looks like your user permission set provided to the user in this company may be restricting the users ability to see data.
Search in 'tell me' Users
Identify the problem user and click their username to bring up the user card

check both the User Group (in the code) and the Company. Noting if you keep the company blank the user will get the Group permission to all companies.
OR
The Permission Set

The same logic applies with keeping the company name blank.
Please confirm if I've answered your question by clicking like and 'did this answer your question = Yes'
Cheers. JC