I have compared the urls from the working pipeline overview and the not working pipeline details:
https://host:5601/app/monitoring#/logstash/pipelines?_g=(cluster_uuid:VTDsWXH0TUqC4YO7H8Zhkw,refreshInterval:(pause:!f,value:10000),time:(from:now-1h,to:now))
https://host:5601/logstash/pipelines/central-syslog?_g=(cluster_uuid:VTDsWXH0TUqC4YO7H8Zhkw,refreshInterval:(pause:!f,value:10000),time:(from:now-1h,to:now))
The problem is that the part "/app/monitoring#" is missing in the lower url. adding this part produces the correct url
Update: Problem will be fixed with 7.8.1 https://github.com/elastic/kibana/pull/69861