Affinity Photo 1.5.0.43 (Beta) should ignore unknown image ressource blocks inside PSD (and PSB) files. Currently it stops the export and shows an error message (unknown signature: psdM [1]). Photoshop simply ignores such blocks (and discards them, so they are not saved by Photoshop). This mechanism ensures older Photoshop versions can read the files of newer versions.
In my case this block contains custom meta data embedded in an image ressource block (3D Data camera position from Autodesk 3ds max). This data is for example used by an After Effects plugin.
PSD file is attached and a screenshot of the error message. This PSD file will import fine in all Adobe applications.
I'm happy to test this again as soon as this is fixed. Let me know if you need any further details.
Daniel
Untitled.psd