I would start with asking them to resend it. If all others are working but one, then what is in common? Nothing. The one is an exception. Have the CLIENT resend it, verfiying no passwords are present, and that they can access it prior to sending. Try to use a NON email method for sending (xdrive or shared drive).
Would suggest you to first open the Task Manager. You can press Ctrl + Shift + Esc buttons together. Go in Details tab and End Task for all soffice listings appearing in it. Now, close the Task Manager and try opening the file in OpenOffice.
Please let us know if you were able to resolve the issue!
First follow the steps suggested by Mr. Ashok because that can help you. If you will get same issue and unable to recover formulas then go for SysInfo OpenOffice.org Math Recovery Tool. Math Recovery Tool is designed to recover all data which were been saved in OpenOffice.org Math ODF file.