Thanks for reporting this issue everyone. We are looking into it but as others have stated the Virtual Switch and Virtual Dimmer Switch are good permanent replacements for the Simulated Switch and Simulated Dimmer Switch with the added benefit that they can run locally on later versions of hub firmware.
When looking at the SmartThingsPublic repo in github be aware that the production branch is the code that has been released to everyone. The master branch and staging branches are used for our internal testing prior to releasing to production. This is the version currently in production: https://github.com/SmartThingsCommunity/SmartThingsPublic/blob/production/devicetypes/smartthings/testing/simulated-switch.src/simulated-switch.groovy.
I’m not sure why health check support was added to these simulated device DTHs (I’m just a Zigbee guy) but from looking at the changes it looks like the devices are supposed to always be online. Perhaps that isn’t working as intended and that’s what is causing the issues with Alexa but I don’t think the intention is for the simulated devices to ever be offline.