Can I assume counterfeit components?
You have to prove the parts are bad.  They may be damaged by ESD.

If you had only pulled the Q5 or Q3 and measured V(Q1-C), that would have isolated the part as the problem.  Then verify R1 is 10k and not 10M or something else.

The only weakness on the design is that the circuit turn off is slow and load reactance is unknown.

Normally any FET (such as this one rated for 8mΩ @ VGS = -10V)  is driven by a gate driver resistance of about 1000x (8Ω as used in datasheet) but your R1/RdsOn ratio is about 10 million. This makes it slow and prone to oscillations with stray inductive/capacitive feedback to gate voltage depending on layout.


also you are putting ~(4V-0.7)/1k=3.3mA into base and and capable of driving >>100mA into gate capacitance Ciss, until Vce is saturated. But pullup to turn off is only 12V/10k = 1.2mA which results in spurious turn off behavior.  More design margin would use 1k for R1 at most.


Conclusion:

Test FETs for ESD damage, leakage in gate as per above. Reduce R1.

There is no assumption as to if/when the ESD damage occurred.

Article on Clone parts.

http://www.sae.org/aaqg/audit_information/2010/Atlanta/Impact%20of%20Counterfeit%20Parts%20NASA.pdf