Pixelmator (v3.8 ) has the ability to center objects with any other objects/layers in the document, whereas Pixelmator Pro (v1.3) does not present as many alignment guides. See video for demonstration: https://imgur.com/qhAvJJq (same file used for both apps). Note that I have "Show guides at object center" and "Show guides at object edges" both enabled on both versions, but Pixelmator Pro does not allow for the same control over centering objects as the original Pixelmator. Any suggestions and/or feedback is much appreciated.
What features would you like to see in Pixelmator Pro?
When it comes to guides, everything should work the same way in both apps, so this could potentially be a bug — could you share that file with us at firstname.lastname@example.org? That would help us get a better idea about what exactly is going on!