See the function const QSafeByteArray QSafeLayoutFileReader::readDataFromFile(const qchar * const filenameArg):
const quint32 maxLayoutFileSize = (Constraints::MAX_ITEM_COUNT*2U*Constraints::LAYOUTDATA_SIZE_V3)+Constraints::LAYOUTDATA_HEADER_SIZE;

The calculated max size for the file is 72728 bytes but in the max capacity test where there are 128 items with fillcolor value and max amount states the file size is actually 327192.
That makes the layout validation to fail.