Argon reboots every few minutes after connecting to the cloud

I have an Argon that has been running fine for months. All of a sudden, it seems to want to reboot every few minutes. When it finally connects, it seems very sluggish when responding to cloud function calls. It’s running 1.5.2. I flashed Tinker to see if it would behave with that app. Tinker didn’t help and it responds very slowly to Tinker (smartphone app) digital write commands (turn D7 on/off). I thought it might be a keys issue and so I ran particle keys doctor once it was in DFU mode, but that didn’t help either.