It was mentioned in the description to NOT upgrade to v3.
Version 2 is still safe and working good. In case you don’t need any new features on your current working project – it’s good to stay with version 2.
We thought that it won’t be a problem if we remove back compatibility to new build, however now I see that a lot of people want it. So we’re investigating how to do it right now.
There is a beta version of migrations. We need few days to test it on all PHP (5.3, 5.4, 5.5, 5.6, 7.0, 7.1) versions with WP 4.7, 4.7.1, 4.7.2.
Also we didn’t check it with multisites yet.
The development was done with PHP 7.0, WP 4.7.2, so with this config it should work fine.
Would be great if you can try and give your feedback:
Please take in mind, that Upload Media and Fields Group fields are still deprecated and we do not plan to return them back. Migration feature creates new Collections based on old settings. However you will need to update your themes in case you use these fields.
We launched new v3.1 with migration feature. Would be great if you can try and give your feedback (update your star rating)