After Mainstage 3.4 upgrade, Cannot open file. The file isn't in the correct format. Is there a way to remedy this?

Yes indeed. Just updated Mainstage to 3.4.1 and my issue has been resolved!! Very happy about that. Thank you.

Update to the just available MainStage 3.4.1 and try again.

Contact Apple immediately via Feedback - MainStage - Apple

There were some Mojave changes regarding security and you might have something special in the concert, which triggers it. It probably still works with MS 3.3.2 _or_ if you use MS 3.4 on 10.13. MS 3.4 and 10.14 Mojave trigger this issue.

Same issue with same hardware/software with me.

It occurs when I introduce midi controlled sliders mapped to master volume and CC.

Replied to a similar issue in another thread. Definitely just started having this problem being on Mojave 10.14.1 and MainStage 3.4. Does Apple look add these threads? I've now corrupted at least 8 of my needed concerts simply attempting to tidy up my layout. The "file isn't in the correct format" happens to me shen I attempt to rename a screen control in assignments and Mappings window. Just renaming the screen control, saving then attempting to reopen is when I get this error. I'm unable to open the concert. If someone on here has a recommendation of how I should attempt to contact Apple about this, it would be most appreciated. This is a big problem for me and is severely hindering my workflow.

MacBook Pro (Retina, 15-inch, Late 2013)

2.3 GHz Intel Core i7

16 GB 1600 MHz DDR3

MacOs - Mojave 10.14.1

Logic Pro X - 10.4.2

Mainstage - 3.4