Metallic Thread - Overview – MELCO Help Center

Run the machine around 900spm.
Use a larger needle. Moving up a needle size means that you have a larger needle eye than normal. This gives more room for the metallic to slide back and forth for the normal sewing process. This creates less abrasion on the thread.
Choose a good brand of thread. Metallic threads vary greatly in quality. Here is where skimping is not a good idea. There have been very favorable reports from customers using both Amann Yenmet and Madeira metallic threads.
Use lighter densities than normal. Metallic thread is usually thicker than normal 40 weight poly thread that most designs are digitized for, and so it needs to be lightened up to keep thread breaks to a minimum.
Increase the tie in and tie off stitch length in the metallic colors of designs. Trim failures can routinely happen using metallic thread. This can be due to a short stitch length for the tie stitches. Since the thread is thicker, the tie stitch length should be increased by several points compared to the normal setting.
Use the metallic trim type setting (Tools>Settings>Trim Type) in AOS Bravo OS, or Melco OS if you have an Original red and white Amaya, an XT, or an XTS. This will give the thread more time in the trim cycle to stretch before being cut which give fewer trim problems.
If a design contains metallic thread that will be embroidered on garments that come in direct contact with skin, it is a good idea to use a fusible cover fabric in the inside of the garment. Metallic thread can be scratchy against the skin.
If you are using Madeira metallic thread, they provide this video that can help you successfully use the thread.
Use newer metallic thread. A test to see if your metallic thread is past expiration is to pull off some of the thread from the cone. If it is very coiled as it unwinds then this is a good sign that it is weak and will give problems when used.
If the situation remains unresolved, you will need additional technical assistance. Here are the available Melco Technical Support options. Consider an NPT upgrade if your machine is compatible.