It's a common problem if you use the higher speed sprockets on the freewheel, or if you put a lot of torque (not "talk") on it from a stop. It doesnt' generally happen except for that.
THere are a number of threads about broken covers, and some have proposed solutions, but the easiest solution is not to put torque into the freewheel when in the higher gears (which are unsupported by any bearings to the axle, and so flex the covers), where the chain is farther from the cover. Shift into a lower gear at the back, and a higher gear at the front, to do the same speed. If you can't, you might need different chainrings or sprockets with the right tooth count to give you the gearing to do this..
If you're already doing this or are otherwise using hte sprocket closest to the cover, then you have to add a bearing.
A much cheaper solution than a $500 custom-made steel cover is simply to put a bearing between the outer end of the freewheel and the axle, so it is supported and doesnt' bend the cover. You could probably do that just by looking around McMaster-carr's site in the bearing section (or asking them), after you measure the outside diameter OD of the axle at that point, and the inside diameter ID of the freewheel at that point. Slip the bearing in there and probably be all done with the problem.
Heck, even a brass bushing would work but it'd have more friction and waste more power as heat. But still cheaper than your new cover (which is still going to have the same problem, though it will probably take longer to show up, or to fail).
One search finds just a single thread
https://endless-sphere.com/forums/search.php?keywords=broke*+cover*&terms=all&author=&sc=1&sf=titleonly&sk=t&sd=d&sr=topics&st=0&ch=300&t=0&submit=Search
but this search
https://endless-sphere.com/forums/search.php?keywords=side+cover*&terms=all&author=&sc=1&sf=titleonly&sk=t&sd=d&sr=topics&st=0&ch=300&t=0&submit=Search
finds a lot more, and I'm sure there are others not found by either search.