What were the problems with colossus?

Colossus, the world's first programmable digital computer developed during World War II, faced several issues including limited reliability due to its reliance on thousands of vacuum tubes, which were prone to failure. Additionally, its programming was complex and required manual intervention, making it cumbersome to operate. The lack of documentation and standardization further complicated its use, and its design was initially kept secret, limiting its potential for broader applications post-war.