https://www.domain.com/sub1//sub2/abc and https://www.domain.com/sub1//sub2/abc/ are technically two different URLs — some applications and web servers might interpret them in the same way, others won’t;
depending on your zone settings, successive forward slashes like // might be normalised to / before redirect phase.
Creating two separate rules works, you could also try changing your wildcard pattern to something like https://www.domain.com/*/abc* since wildcards can match on zero or more characters, meaning that both URLs /abc and /abc/ (but also /abc/123, keep that in mind) will redirect.
@ncano thanks for your reply. Looks like I will keep two separate rules.
In this case, the requested URL should be like “end with” /abc with or without / at the end so I guess https://www.domain.com/*/abc* won’t be used.
Thanks again for helping me learn about with or without / are technically two different URLs and wildcards can match on zero or more characters