The latest PowerApps Version is 2.0.461. Were you using the latest version?
I was using PowerApps Version 2.0.461. I had an App(I created at previous version), it was connecting to SharePoint Online and contained an Edit form and Display form. I opened it on Preview mode, the forms were shown well. Then I opened it on View mode on PC, iOS, and also Web player, all were worked well. I also created an App at current version which had a connection with SharePoint Online, the forms can be shown in both Preview mode and View mode on PC, Web player, iOS.
Please check your PowerApps Version, if you version was not the latest version, please update it and have a try again.
Community Support Team _ Mabel Mao
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