The material is likely a very small piece of white cartridge septum that was cut out by the syringe needle and drawn into the syringe.
The chance that the cartridge septum material can be pushed back out of the syringe and into the cartridge is small. It is okay to use the syringe even if white septum material is observed.
Be sure to use the syringes and needle tips that come with your t:slim X2 cartridges. If you believe your cartridge box is missing the included syringes or needle tips, check for them underneath the inside flap of the cartridge box.
Make sure you are using proper load technique.
Load a Cartridge Quick Reference Guide (PDF) >
Always refer to the User Guide for important safety information and detailed step-by-step instructions on how to load a cartridge. Please consult the applicable user guide and refer to the table of contents.