Ni no ito keeps breaking

Hello, I started playing shamisen in November this year in Japan. However my ni no ito has been breaking very frequently.
I have a background in guitar so when I say frequently I guess I mean compared to that. also most strangely to me is that it always breaks between the itomaki and the neck while in it’s case.

my teacher likes for me to play in C# so that’s where I have it the majority of the time.
the room I keep it in is usually around 50% humidity, 20 celsius. I play for 30min-1.5hours basically every day.

what’s driven me to post now is that I only just replaced it last time 2 weeks ago. it doesn’t always break this quickly but i think I’ve already replaced my ni no ito probably 5 or 6 times since november when I started. also the ni no ito is the only string that ever breaks. i’ve only replaced the others when my teacher suggested it.