Hmm. I got the same error as in Major Issue with 2018, and the workflow definitely did not run.
What you describe did not happen. Everything was definitely broken, including a simple workflow with only a Message Box. The reinstall fixed it, though.
Regards,
burque505
ashokkarale
MD_Farhan1
Ajay_Mishra
postwick
Dheerendra_vishwakarma
Anil_G
chandreshsinh.jadeja
Gautham_Pattabiraman
vrdabberu
aravindbalineni123