Heads Up :
The post you are writing will appear in a public forum. Please ensure all content is appropriate for public consumption. Review the employee guidelines for the community here.
Also running 8.5.135.0 and experiencing this bug via the GUI.
However, adding the community via the CLI functions correctly:
config snmp community create COMMUNITY
config snmp community accessmode {ro | rw} COMMUNITY
config snmp community ipaddr IP...