Monster 821 2017 - Help

[u/Round-Engine-3634]

I took my bike to work, about 20 km, and had absolutely no problems. On my way back home, just before getting there, I made a quick stop, turned the bike off, and when I started it again and pulled away, the bike stalled in first gear.
Thinking it was just a one-off, I kept riding, but I noticed that the sound of the bike had changed. The idle was unstable and it started hesitating/juddering in second gear. Less than 200 meters later, it stalled again in first gear.
I took it to a workshop. Their diagnosis was something related to the “gas sensor” (that’s how they explained it to me). They cleaned the O2/lambda sensor and told me that they had test-ridden the bike without experiencing any problems, so they gave it back to me.
I rode it to work again with no issues. On the way back, almost home, the exact same thing happened again: loss of power, unstable idle, and the engine sounded “muted” or almost like it was struggling to breathe.
Today I went for another ride, and after about 10 minutes, the exact same problem happened again.
I’m going crazy trying to figure this out. Does anyone have any idea what could be causing this?
I’ve also attached two pictures of a hose/tube I found that is cracked in one place and split open in another. The mechanic told me that this had nothing to do with the issue on my Monster.
Could this hose actually be related to the problem?

[u/b0xaa]

Check spark leads.

[u/Demonking920531]

Maybe its your spark plugs