Hi,
Did you update your macOS version to 10.15 recently? The 10.15 version just came out recently as a developer beta build, and as of yet is not stable; this being the case Axure RP is not yet expected to run smoothly on it until we’ve had more time to test, identify, and resolve issues. We would advise not updating the OS to any beta builds early on or until they have stabilized to help avoid running into show-stopping issues that arise from unexpected bugs.
We’ll be investigating more on our end, but for now the latest macOS version we’d advise using would be one of the 10.14 builds to ensure that Axure RP is stable. Thank you!