If I factory reset the CRS326-24G-2S+, it defaults to RouterOS. OK, good.
If I then set the boot to SWOS, it boots with the old SWOS config. Not a default SWOS config.

A stupid engineer put a bad SWOS config on this switch and it is impossible to access using http.

How can the SWOS config be reset to factory default?

I'd try via console cable, and then via netinstall if the first approach fails.

Yes, Mikrotik support replied to my email with:

Please connect to device via serial console. Boot SwOS and choose "r - reset configuration". This should reset SwOS configuration to default. Also we will improve our manual.

This switch is remote to me and the tech onsite has no console cable. So for now, I'm just using RouterOS.

It would make more sense for the push button to default the config of the OS selected for boot....
If SwOS is boot OS then reset SwOS if button pressed, etc.

you can factory Reset SwOS just with simple let see on my blog post, this using indonesian Lang, u can translating this article

https://agungjies.web.id/cara-reset-fac ... otik-swos/

Since RouterOS 6.43rc29 it is possible to load, save and reset SwOS configuration, as well as upgrade SwOS and set an IP address for the switch by using RouterOS.
You could try to reset SwOS configuration with a command:
/system swos reset-config

Also, try to upgrade SwOS to latest available version (you will need an access to the Internet):
/system swos upgrade

See more details at this article: https://wiki.mikrotik.com/wiki/SwOS/CSS ... g_RouterOS
Note that release candidate versions are published strictly for testing purposes and should not be used on production routers.