In the class definitions it is possible to nest a LocalizedField in a Block. Objects of that class can be opened and saved without any problems. But as soon as any data field in the LocalizedField contains any data, the object panel of the Pimcore backend UI breaks.
Also the folder preview and the folder tree preview no longer work when such a "corrupt" shall listed.

Pimcore X v10.0.0

The stack trace:
Fatal error: Uncaught TypeError: Cannot assign Pimcore\Model\Element\ElementDescriptor to property Pimcore\Model\DataObject\Localizedfield::$object of type ?Pimcore\Model\DataObject\Concrete in /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php:252
Stack trace:
#0 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php(252): ReflectionProperty->setValue(Object(Pimcore\Model\DataObject\Localizedfield), Object(Pimcore\Model\Element\ElementDescriptor))
#1 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php(208): DeepCopy\DeepCopy->copyObjectProperty(Object(Pimcore\Model\DataObject\Localizedfield), Object(ReflectionProperty))
#2 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php(144): DeepCopy\DeepCopy->copyObject(Object(Pimcore\Model\DataObject\Localizedfield))
#3 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php(252): DeepCopy\DeepCopy->recursiveCopy(Object(Pimcore\Model\DataObject\Localizedfield))
#4 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php(208): DeepCopy\DeepCopy->copyObjectProperty(Object(Pimcore\Model\DataObject\Data\BlockElement), Object(ReflectionProperty))
#5 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php(144): DeepCopy\DeepCopy->copyObject(Object(Pimcore\Model\DataObject\Data\BlockElement))
#6 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php(94): DeepCopy\DeepCopy->recursiveCopy(Object(Pimcore\Model\DataObject\Data\BlockElement))
#7 /var/www/html/vendor/pimcore/pimcore/models/DataObject/Data/BlockElement.php(241): DeepCopy\DeepCopy->copy(Object(Pimcore\Model\DataObject\Data\BlockElement))
#8 /var/www/html/vendor/pimcore/pimcore/lib/Cache/Core/CoreCacheHandler.php(594): Pimcore\Model\DataObject\Data\BlockElement->marshalForCache()
#9 [internal function]: Pimcore\Cache\Core\CoreCacheHandler->Pimcore\Cache\Core{closure}(Object(Pimcore\Model\DataObject\Data\BlockElement))
#10 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/TypeFilter/ReplaceFilter.php(28): call_user_func(Object(Closure), Object(Pimcore\Model\DataObject\Data\BlockElement))
#11 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php(125): DeepCopy\TypeFilter\ReplaceFilter->apply(Object(Pimcore\Model\DataObject\Data\BlockElement))
#12 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php(155): DeepCopy\DeepCopy->recursiveCopy(Object(Pimcore\Model\DataObject\Data\BlockElement))
#13 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php(135): DeepCopy\DeepCopy->copyArray(Array)
#14 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php(155): DeepCopy\DeepCopy->recursiveCopy(Array)
#15 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php(135): DeepCopy\DeepCopy->copyArray(Array)
#16 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php(252): DeepCopy\DeepCopy->recursiveCopy(Array)
#17 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php(208): DeepCopy\DeepCopy->copyObjectProperty(Object(App\Model\Product\Car), Object(ReflectionProperty))
#18 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php(144): DeepCopy\DeepCopy->copyObject(Object(App\Model\Product\Car))
#19 /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php(94): DeepCopy\DeepCopy->recursiveCopy(Object(App\Model\Product\Car))
#20 /var/www/html/vendor/pimcore/pimcore/lib/Cache/Core/CoreCacheHandler.php(605): DeepCopy\DeepCopy->copy(Object(App\Model\Product\Car))
#21 /var/www/html/vendor/pimcore/pimcore/lib/Cache/Core/CoreCacheHandler.php(910): Pimcore\Cache\Core\CoreCacheHandler->storeCacheData('object_81', Object(App\Model\Product\Car), Array, NULL, false)
#22 /var/www/html/vendor/pimcore/pimcore/lib/Cache/Core/CoreCacheHandler.php(958): Pimcore\Cache\Core\CoreCacheHandler->writeSaveQueue()
#23 /var/www/html/vendor/pimcore/pimcore/lib/Cache.php(200): Pimcore\Cache\Core\CoreCacheHandler->shutdown(false)
#24 /var/www/html/vendor/pimcore/pimcore/lib/Pimcore.php(240): Pimcore\Cache::shutdown()
#25 /var/www/html/vendor/pimcore/pimcore/lib/Kernel.php(242): Pimcore::shutdown()
#26 [internal function]: Pimcore\Kernel->Pimcore{closure}()
#27 {main}
thrown in /var/www/html/vendor/myclabs/deep-copy/src/DeepCopy/DeepCopy.php on line 252