I got the same issue, and played a bit with. For me it all started a bit more than week ago, when I updated the bios to the most recent one provided by Lenovo...
Ctrl+Shift+Esc brings up the Task Manager, and before it crashes on the Processes tab the memory usage is ticking up, roughly 1% per second -- and after 99% comes the freeze. (I have a T450 with 16GB RAM, and once it starts ticking up, I have more than a minute to get prepared for the crash.) I have admin rights and although I kill all apps and basically every process which I can kill, the memory usage keeps ticking up, unstoppable...
But, once I cut my internet connection, whether turning off the wifi on the notebook or shutting down my router, the flooding of my memory stops and even a very slow recovery begins. Better still: if I turn the wifi back on, the situation stabilizes; though the memory consumed up by then remains unavailable, or recovers just very, very slowly.
Today there was a somewhat similar issue with Epson printers and Google Cloud Print (GCP): my printer was usable for about only 20 seconds, then it froze and restarted, and the solution was to cut it off the net. It turned out to be an issue with GCP, which needed to be de-activated on the printer -- either within 20 seconds or by internet connection cut off. Once GCP is suspended, the internet connection can be re-established, without the freezing. hat tip to user forums...
unfortunately I could not find solution to this Lenovo issue.
I had a chat with Lenovo (as my notebook is under warranty), and they proposed to reinstall windows; which actually helped -- for a few days, after which the problem started again. Now that I learned this cut-off-and-turn-back-on-the-internet-connection trick, I can manage... but it is certainly not the user experience I was after when buying a professional grade notebook for home, just exactly NOT to have this kind of issues.
Anyway, if your hardware turns out to be fine, try having a look at your memory usage in TaskManager or ResourceMonitor; and try to play with cutting the net connection.