This usually happened when current push or deployed code is contains error. Best thing to do? revert to previus commit.
git log
// the following logs appear and choose which to use e.g
commit 31eb090365b9d177880f66beee2312ad2e130e3a (origin/master, origin/HEAD, master-bak, master)
//checkout to new commit point to revert temporarily
git checkout 31eb090365b9d177880f66beee2312ad2e130e3a
Another method is, create bak branch e.g
git branch master-bak
//once master is bad, checkout to master-bak, the previous state of commit.
