This same issue happens with me also.
Actually, a feature called MPP is behind this partially filled orders.
I raised request to give us option to disable MPP (like Zerodha) but they are not listening.
@AngelOne Please listen to traders. Give us option to disable MPP. This feature causes lot of problems.
Learn from Zerodha, they give option to enable/disable MPP, otherwise we have to close our accounts and shift to other brokers.