I still cannot reproduce it in your system:

[test@ixion-pld cpython]$ hostname
ixion-pld
[test@ixion-pld cpython]$ uname -a
Linux ixion-pld 5.5.2-1 #1 SMP Wed Feb 5 19:26:43 CET 2020 x86_64 Common_KVM_processor PLD Linux

[test@ixion-pld cpython]$ cat lel.py
from multiprocessing.pool import ThreadPool
class A(object):
    def __init__(self):
        self.pool = ThreadPool()
    def __del__(self):
        self.pool.close()
        self.pool.join()
a = A()
print(a)
[test@ixion-pld cpython]$ time ./python lel.py
<__main__.A object at 0x7f9130becd20>

real    0m0.124s
user    0m0.105s
sys     0m0.021s