OnePlus Nord CE 4 randomly shuts down at 20–50% battery. Anyone else experienced this?

I'm facing a weird battery issue on my OnePlus Nord CE 4, and I'm wondering if anyone else has experienced the same thing.

The phone drains normally from 100% down to around 50%, but below that it becomes completely unpredictable.

It has:

• Shut down at 50%
• Shut down at 29%
• Earlier it used to shut down around 20–25%

The percentage where it dies isn't consistent.

The strange part is that after it shuts down:

• It won't turn back on.
• Pressing the power button does nothing.
• I have to connect the charger before it will boot again.
• After booting, it usually shows 0–5% battery and then charges normally.

I've already tried quite a few things:

• Full discharge/full charge cycles
• Battery calibration attempts
• AccuBattery
• ADB diagnostics (dumpsys battery, batterystats, etc.)

Software diagnostics look normal:

• OnePlus battery health shows 95%
• No battery hardware errors in ADB
• No overheating
• Phone works perfectly above ~50%

So I'm starting to think this isn't a software issue but something related to the battery, battery management system (BMS), or power management hardware.

Has anyone with a Nord CE 4 (or any recent OnePlus phone) had this exact issue?

• Did replacing the battery fix it?
• Was it something else?
• Is there any known OxygenOS bug that causes this?

I'd really appreciate hearing your experience before I take it to a OnePlus service center.