can you do a static NAT using the same public ip so that it goes to different internal ips on different port numbers.? Something like a port-redirection. For example, the public ip:100.100.100.100/443 goes to 10.10.10.1/443 AND 100.100.100.100/8443 goes to 10.10.10.2/443.
Yes, since we are doing Auto NAT / Network Object NAT (the ones configured under "object" configurations) that means the ASA will order the NAT rules based on predefined rules.
I think in your case it comes down perhaps to the last determining factor which is the "object" name (alphabetical order). They are otherwise the same but the other one ends with "1" and the other one with "2". This is why the "websrv1" one is working.
But this is NOT the actual problem. I think you have the ports configured the wrong way around.
The first port listed after the "service tcp" or "service udp" should be the local/real port. This is the port that is actually listening on the host/server. The second port listed should be the mapped/public port.
So the NAT under the "object network websrv2" should be
nat (to-nexus,Outside) static 100.100.100.100 service tcp https 8443
Try that and see if it works.
Notice that you can use the "?" after the "tcp" section of that command which will list if the next expected value is the real/local port or the mapped/public port.