Hi @John Guilbert ,
Due to the restricted testing environment, I can not deploy SharePoint mobile app in SharePoint server 2019.
Here, I would like to confirm more information with you for further troubleshooting:
1) Does the issue occur on the side panels of other sites or only on one site?
2) Do other users experience the same behavior?
3)Try to uninstall OneDrive in mobile phone then check the result.
In addition, if the issue is more related to ShareGate, then this is a third-party app and out of our support scope, we suggest you get support through https://sharegate.com/support.
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