Something wrong with your install or shortcut mapping, maybe? It definitely does work in 2018.2 and all the lower versions (well, at least since it's called Graphite tools, not sure about Polyboost history). There are some other tools that don't though, and the main reason is laziness. Same with the scripts, most of the time, you'd have to write two versions, a different one for each. Which is why I released a polyModOp library some time ago. It mirrors polyOp methods, so if you stick to them when writing a script, making it work with edit_poly as well is a matter of just a few additional lines of code.
I'm using quite a few macro scripts, but swift loop is assigned from Main UI... I don't know anything about max script, just a maya modeler trying to get up to speed in max.. so much customization required......I'll try uninstalling 2018.3...
I might be to late, but try to do a "Factory reset". I will leave you a link on how you can do that. You will lose your keybindings and settings in the process, but it's worth a try. If you keep the current ENU folder, you can always restore your settings back again if wanted. Keep in mind, this so called Factory reset will reset most things in 3Ds max, but not everything.
EDIT: Also, if you decide to uninstall 3Ds Max for a reinstall, make sure you remove all traces. Clean your registry and all folders created with 3Ds Max. This will of course be a very tedious process, but ensures that the next install will be clean and hopefully work as intended.
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https://www.youtube.com/watch?v=Rb0nqMjBaEY
EDIT: Also, if you decide to uninstall 3Ds Max for a reinstall, make sure you remove all traces. Clean your registry and all folders created with 3Ds Max. This will of course be a very tedious process, but ensures that the next install will be clean and hopefully work as intended.