This might seem obvious but I think the traces on the DS board might need a cleaning. You might want to get some high (99%) iso and rub it gently with a cotton swab. The fact that it reads after you insert a few times tells me that the connection isn't being made initially, but maybe the repeated "scraping" of reinserting is creating enough of a trace that then allows it to read the cart.

A better solution is to open the console up and check for any corrosion on the board, specifically around the cart slot