Command sfdx force:org:display --json sometimes provides the "instanceUrl" with a trailing and other times it does. Appears to be about 50/50 from anecdotal testing.
sfdx force:org:create with different aliasessfdx force:org:display --json -u <username> for each of the aliasesThe instanceUrl's value will either always have a trailing / or will never have a trailing /.
i.e. https://ruby-energy-5366-dev-ed.cs26.my.salesforce.com/ & https://power-force-9974-dev-ed.cs91.my.salesforce.com/
This is intermittent (perhaps dependent on instance like cs26 vs cs91) but depending on random chance some will have / and others won't
i.e. https://ruby-energy-5366-dev-ed.cs26.my.salesforce.com/ & https://power-force-9974-dev-ed.cs91.my.salesforce.com

SFDX CLI Version(to find the version of the CLI engine run sfdx --version): sfdx-cli/7.52.0-c5ad5c3eff darwin-x64 node-v10.15.3
SFDX plugin Version(to find the version of the CLI plugin run sfdx plugins --core)
OS and version: macOS 10.15.4 (19E266)
Ya, I consider this a bug and something we noticed a little while ago. FYI @shetzel
Ya, I consider this a bug and something we noticed a little while ago. FYI @shetzel
@amphro @shetzel thanks yeah I assume this isn't a bug in CLI as much as however the CLI is being served, but it would be nice for the CLI to standardize it for us, so from that perspective it would be a feature I suppose.
This should be fixed in the new open-source version. You can try it early, here: https://github.com/forcedotcom/cli/issues/835
I'm closing this--reopen or log another issue if you see any more trailing slashes.