I know one way I always fix issue like this is by replacing below file on mgmt server from one that works:
[Expert@cpazuremgmt:0]# cd /web
[Expert@cpazuremgmt:0]# cd conf
[Expert@cpazuremgmt:0]# ls
extra httpd2_mp.conf mime.types server.key
httpd2.conf login server.crt
[Expert@cpazuremgmt:0]# cd extra
[Expert@cpazuremgmt:0]# ls
httpd-ssl.conf httpd2-smartview.conf
httpd2-bl-tp.conf httpd2-smartview.conf.backup_R80_20
httpd2-cpextensions.conf httpd2-webapi.conf
httpd2-cpm-saml.conf rest-api.conf
httpd2-mwc.conf ssl
[Expert@cpazuremgmt:0]#
I dont sadly have R81.10 lab server myself, only R81.20, can send you that if you want to try, cant guarantee it would work, but you can give it a go, just backup current one.
Let me know.
Andy