From the #BetterLateThanNever file…
Propellerhead has announced that Reason Users SHOULD NOT UPGRADE to MacOS High Sierra 10.13.4 due to a negative impact on the application’s performance:
Dear Reason user,
It has come to our attention that the latest macOS High Sierra 10.13.4 has a negative impact on Reason’s performance. Currently we do NOT recommend you to update your macOS High Sierra to 10.13.4 if you are using Reason.
We’re on it and hope to get to the bottom of this as soon as possible.
Note: Mac OS High Sierra is only supported in Reason 9.5.2 and later, including Reason 10, Reason Intro & Reason Lite.