Clone step fails often

The clone step fails quite often when the build is started over a github hook. If I restart the build just a few seconds after the fail it doesn’t fail. Any idea where/how I can investigate the problem further?

+ git init
Initialized empty Git repository in /drone/src/
+ git remote add origin
+ git fetch --no-tags origin +refs/pull/18516/merge:
fatal: Couldn't find remote ref refs/pull/18516/merge
exit status 128


Duplicate of [SOLVED] Issues when cloning github PR