In my case, this is somehow related to having https in the VA ACARS URL parameter when you setup a connection in SIM ACARS. What is really odd though is that it was originally working with https but then stopped working.
My hosting company upgraded the PHP by one patch, from 7.0.26 to 7.0.27 and then SIM ACARS stopped connecting with https. I changed it to http and it works. I have no idea why and my hosting company says they changed nothing other than patching the PHP.
On my test site here, I am running PHP 7.1.10, but since it is a test site, I am not using SSL with it. I switched my PHP version on my live site from 7.0.27 to 7.1.13, but connecting with https still doesn't work. So, something else changed with my host that is affecting this.
So, I have no idea what happened or why it suddenly broke. My hosting company, of course, says it's something I did, even though I changed nothing on my end. On Tuesday, everything worked fine and a couple of us few flights. When I got home from work on Wednesday, SIM ACARS didn't connect anymore. I changed nothing, but they changed something, but apparently, it's my fault. You gotta love tech companies, don't you?
My point to this post is that, if you are using SSL on your site, you should still leave the VA ACARS URL parameter in SIM ACARS as an http link and not https, otherwise you might start seeing the errors listed in this thread. I hope this helps someone.
Cheers,
Glen