Hi Mike,
First, this is tough to troubleshoot, because even though there are three or four people having similar issues, they are different issues, and there are four out of many. So, you have a multitude of variables. Different client OS, different hardware, laptops with home versions, etc. We still don't know your actual bandwidth between computers. The interesting thing in your situation is that the one where bandwidth shouldn't matter is the main computer. And, it is more than reasonably powered. The other variable is you are running 9.4.2 as most above, and this is going to be the most likely version to have issues.
As I say all the time, and I guess most don't agree, is you just shouldn't be using your main computer with AC or anything. Not sure from your post if it just crashes or if it crashes, because you are using it. Is computer properties in Advanced set to background services or programs. Of course, that is a non-issue if you are using the Main Computer. Again, looking at the AcroPDF.dll error, have you run the computer with that program completely shut down? In troubleshooting, it is helpful make one change at a time and isolate problems by removing them from the equation.
It is also strange to some degree that you lost all connectivity just by rebooting the main computer. What Indy is suggesting is not to reboot, although you can, but simply to type services.msc in your search box or run box, fine SQL for AC, and restart it. Not completely sure how the connectivity is set up there, but if you haven't changed anything, then it is likely under system. There is a problem if you have to go to all that trouble to reconnect each computer. We also have the added problem of wireless, which will always be an added problem in every network that has wireless. Period.
One thing I can tell you with 100% certainty is that with v9.4.2, and running the default setup, you are using SQL Server Express 2012. You are not running Standard. Unless you recall a) shelling out $500 to $600 for standard, then more money for licenses and then finding some type of SQL guru to set up your new AC instance on the standard SQL, you are running Express. And, with your setup, you don't need anything more than Express, and while I understand Indy's suggestion as just more more troubleshooting step, you shouldn't need to clear it daily.
The fact that the issue is on your main computer, where you are running AC directly to SQL, which should give you nearly no latency, it says volumes. Either about the version of AC or something to do with that computer. This is where running a server with Hyper-V, with AC on a single VM is helfpul. Just give up on 9.4.2 and click on 9.1 checkpoint, and you are back to 9.1. Of course, you would need a good backup, and God only knows if you can restore it without the help of AC. One of the main reasons I don't upgrade anymore.
I can't find the post, but one person on one of these threads reported back last week that he had fixed the issue after troubleshooting quite a long time by purchasing a new computer with high specs after he had purchased a new switch. I don't think he is using it as a client. I can't suggest enough not to use your main computer as a production computer. For one thing, you can set up the new computer with the latest CPU from AMD, give it at least 16GBs of RAM, set for background services, check the use for best performance, maybe run an A/V, and only run AC. Then run one computer directly to the new computer and see how it runs. The worse case scenario is you get a brand new computer to run as a main.
FYI: Rather than use task manager to monitor performance, you may want to use perfmon or, even better, Process Explorer:
https://docs.microsoft.com/en-us/sysinternals/downloads/process-explorer
