There have been quite a few instances of the round tongue of the trailer cracking. Most are from towing behind a vehicle with the trailer hitch mounted way behind the axle. Primary culprits are RVs.
The thought: If when you pull into a gas station or other driveway the trailer tongue hits the ground, it's trying to support the tow vehicle and can't. There's a temptation to use a low drawbar so the tail of the trailer sits up high and doesn't hit the road in these situations. If you want the tail higher, put a lift kit on the trailer (spacer between axle and trailer body) and keep the trailer level.
My current trailer had a cracked tongue, and it has never been towed behind an RV. Replaced with the newer square tongue available at Williams.
Hope this helps,
Jim