That production rate is less due to slowness, but more due to low numbers of helicopters. Which is understandable, not many countries out there buy attack helicopters. Except for AH-64, every modern attack helicopter out there can be classed as export failures by most metrics. AFAIK, TAI didn't face any delays in T129 delivery to any users for the last decade.
Let us start with Nigeria:
Nigeria experienced initial delivery delays for its 6 t129 order. They had to use diplomatic push to kick TAI in the back to get their t129 helicopters in October 2023.
Philippines t129 order:
TAI took the contract for 6 units without confirming availability of export licence for their engines. That delayed initial batch deliveries.
Whereas the contract was supposed to conclude in early 2023 it actually concluded with the delivery of last 2 helicopters in November 2023.
Turkish orders:
Apart from qualification and technical failure delays of initial batches which took time to sort out, the production rate was abysmally slow. Then TAI MD boasted about two helicopters per month production rate. Yet they only managed 7 in a year inspite of the fact that they had 60 units firm orders in hand with an option for further 40 units by 2010 for domestic use only.