New Salesforce Release. Preview sandbox vs non preview sandbox.Three times per year Salesforce.com comes out with their feature releases. These releases contains lots of new features and changes. Before any production org is updated to the new release, Salesforce allows you to upgrade the sandboxes you chose to the new release (Preview sandbox).
There shouldn't be any problem when using Copado with preview sandboxes and non preview sandboxes. Copado will use the old API version until Salesforce upgrades all the environments to the new API version.
Now, according to Salesforce best practices, you should never deploy from preview sandbox to a current release version and this is applicable to all environments not only production environment. Since the newer version has new code base, changes to methods, Apex handling, flow automation and many other areas, Copado might be affected by changes introduced by Salesforce´s side in the new release.