The Unable to get local issuer certificate. <20> error is observed when starting published apps:
The issue also might be observed when upgrading from previous RAS versions to v17.1 or later.
Missing an associated intermediate certificate in the RAS console.
NOTE: It should be a one time issue due to a significant change in the way of storing certificates in the product starting from v17.1
1. Go to RAS Console ⇒ Farm ⇒ Certificates ⇒ Open certificate Properties from the context menu and switch to Intermediate Tab.
2. Check if it is empty, copy the intermediate certificate to this tab and apply the settings.
Please refer to the article for the steps to extract the intermediate certificate: https://kb.parallels.com/en/122996