Also, it’s not just a display problem, because they aren’t working in the related automations either, whereas the other ones that I created at the same time are showing properly, and working just fine in automations.
I even deleted the ones that are exhibiting this problem, recreated new ones, and just those two devices are STILL showing this “Checking…” status in the SmartThings mobile app.
Any idea why this might be happening?
I had a similar issue recently and started tapping on the “checking” on the tile, going into the device through the app and looking at history, and pretty much anything else I could review. After that, it just started working. No idea why, but you’re not alone.
Are these devices using the stock Simulated Contact Sensor types? It would be perfectly normal for them to show Checking ... when first created as the contact attribute hasn’t been initialised with a value. They would normally show a broken cloud icon on the detail page too.
However they should sort themselves out as soon as an open() or close() command is used on them in webCoRE and that sounds like it is where you have the issue.
They are still using the built-in, default device handler (I did not modify them to use any other handler at all yet).
If I understand properly how things work, the issue is not with webCoRE.
The ones not working are simply not working right inside of the SmartThings mobile app, regardless of anything else outside of or connected to SmartThings.
i.e. I created this thread hours ago, and had to set it aside to go work on other tasks.
I just checked now, and the two simulated contact sensors that weren’t working before, and were displaying “Checking…” in the app are still not working, and still displaying “Checking…” as of right now.
Good thing is that I’m NOT freaking out. lol
I’ve been doing this stuff for way too long to go there.
Usually, it’s some little quirk that I just don’t know yet, or maybe even a legit glitch in the soup somewhere.
Having other peeps willing to wade through it with me sure helps. So, thanks, guys.
I know it will get resolved eventually…
UPDATE:
I just went back through everything one more time…SmartThings mobile app, IDE, webCoRE, Alexa Routines, and discovered that the two that were still not working got reset or something, and weren’t connected to either webCoRE OR Alexa. 
I walked through getting them both connected to both webCoRE AND Alexa (AGAIN! lol), and now they are working…
->KeyFob button press
->webCoRE opens simulated contact sensor
->Alexa reacts to that, and a Routine does what it’s supposed to do
YAY! 
Thanks again, guys! 
For my next FibFob adventure,
tomorrow I will be troubleshooting multi-presses… 