V1 output is abnormal as below waveform:
How can I thoroughly solve the problems I am currently facing?
if you want to get more information,please let me know.
This diagram explains the softstart conditions highlighted above. If all conditions are met, V1 starts powering on and enters the M5 timing sequence, which takes 150-500µs. If the startup fails within this time, it enters the FS state and restarts after 100ms. This is roughly the process.
Could you please explain the softstart process?
This section, " 19.4.6 V1UVLP monitoring chapter shows 'V1 is also monitored for V1UVLP when the device powers up after a wake-up from LPON, and during a cold start after TSOFT_START_V1. If, at the end of the softstart, V1 is still under the V1UVLP threshold, then the device goes into Fail-Safe state.'" What exactly is required for the V1 startup waveform?
Thanks
This problem is most likely caused by V1 experiencing a startup failure during the soft boot process of OC, followed by a recovery.
The solution is to add an external tube to the V1 port and enable this function when using FS23 OTP, or you can choose our HVBUCK version.
Alternatively, you could remove some output capacitors to make the softstart smoother. I recommend choosing either of these two solutions for greater stability.
1: If PIN37 in the schematic is not used, ground it.
2: V1's load current is not large, only a maximum of 100mA. Please confirm the load at your location.
3: The decoupling capacitor of V1_IN is 1uF.
4: In the case above, if the first startup fails and the second startup occurs, can the register M_GEN_FLAG be read to see what happened?
Let's change these things first and see the results.
We measured a new waveform and found that V1 sometimes fails to start on the first try when the input is 12V.
This is the waveform of the first startup failure. 
This is the waveform of the second successful startup. 
Is this related to the undervoltage detection in V1 after a soft boot? The typical soft boot time is 300µs, and the maximum is 500µs. Why does it seem like it won't boot if it exceeds 500µs, but it seems to work if it's below 500µs?
Could you please describe the soft boot process? The manual doesn't provide much information about it.
With 8V Vin, could you reduce the time axis of the waveform circled above? I want to see how long V1 has been running.
Can we also test the same waveform with 12V VIN?
I don't have a high and low temperature test chamber here, so I can't do too many tests. I can only rely on your results.
You can see below circled part.
current test results show VBOS>3.06V TO V1 UPing used 13.2ms, please check
A lots of confuse for your test result ,you can see when Vbat< Vsup_uv,the V1 should be stay 0,why your V1 follow up VBAT from 0? I suppose your test waveform yellow is VBAT,Green is V1,am I right?
This is testing.
by the way, we check the manual and found 19.4.6 V1UVLP monitoring chapter shows "V1 is also monitored for V1UVLP when the device powers up after a wake up from LPON, and during a cold start after TSOFT_START_V1. If, at the end of the softstart, V1 is still under V1UVLP threshold, then the device goes into Fail-Safe state."
does it mean V1 should beyond V1UVLP threshold after TSOFT_START_V1(type,300us)?
in addition ,this V1 abnormal issue happened in low temperature (-30℃ ） and low Vsup power(8v)。in this condition, we increased VSUP to 12V，V1 output OK。
You can try to disconnect MCU with V1 and test it again for example add some loading 50mA.