Sandeep you gave me a JSON to try
"http://downloads.arduino.cc/PR/samd/package_samd-b84_index.json"
But when I was looking at some of your GIT comments I noticed you had updated to
"http://downloads.arduino.cc/PR/samd/package_samd-b86_index.json"
I added that so that right now I have the following.
"boardsmanager.additional.urls=http://downloads.arduino.cc/packages/package_mkr1000_index.json,http://arduino.esp8266.com/stable/package_esp8266com_index.json,http://downloads.arduino.cc/PR/samd/package_samd-b86_index.json"
And BTW this seems to be working quite well with the DHT sketch and has not failed for over 36 hours since I added your current JSON.
My concern is that I have two packages for the MKR and I was unsure if I should remove one ?
Am going to wait and see if this newer JSON fails before I change to a TMP based sensor to follow your other advice. I have no idea what you changed in "samd-86" but I have a sneaking suspicion that you may have nailed it.
EDIT / UPDATE
Now over 48 hours and zero issues. I have had the regular IDE serial console open all this time too so I am going to turn that off for another test run... Wish me luck...