Try this,
Download nightly build 64 bit and add these settings,
https://support.smartbear.com/downloads/readyapi/nightly-builds/
In your Ready API installation folder, in the Contents directory, please find the vmoptions file and open it in a text editor.
Add these lines to the file:
Edit the vmoptions file in Ready API Pro installation folder\bin folder for windows and for Mac Applications/Ready-API-Home.app/Contents/ to accommodate following changes,
Set Xms128m and -Xmx to 4000 if your ram is 4GB or 8000 if its 8GB
-XX:MaxPermSize=128m
-XX:MinHeapFreeRatio=40
-XX:MaxHeapFreeRatio=70
-Dsoapui.jxbrowser.disable=true
-Dtest.history.disabled=true
Once you do this, go to .readyapi folder in user folder > delete the contents of the db directory.
Close and restart Ready API