The dual silk is supposed to be slightly oval. Per customer service when I opened a ticket:
“To ensure that the filament does not rotate during the printing process and thus provide the dual-colour effect, the filament of PLA Silk Dual Color is designed to be oval instead of circular; that is, its average diameter is 1.75 mm, and the actual value is mainly in the range of 1.60 mm to 1.85 mm.”
However, my measurements showed 1.8mm by 1.5mm. Sent video of it failing to load and received a refund. I will try a different dual-color brand in future but all other Bambu filaments work for me, no issue. May be a defective batch.