Boot OS delay on RHEL7.3

I have installed docker-compose 1.24.0 with pip on RHEL7.3
I encountered the problem that OS startup is delayed about 30 minutes.
This problem always occurs. Please tell me the cause and the solution?

What I tried:

docker[ssh] 3.7.3 was installed as a dependency package of docker-compose.
So I tried to install docker[ssh] 3.7.3 on the RHEL7.3 server without docker-compose python package.
I restarted the server then the slow boot problem was occured.

The following is strace, I think that the startup os is delayed due to cryptography polling processing:

    444   07:46:10.109640 [00007f72c2ebfa10] open("/usr/lib64/python2.7/site-packages/cryptography/hazmat/primitives/kdf/scrypt.pyc", O_RDONLY) = 13 <0.000040>
    ...
    444   07:46:10.114567 [00007f72c38afc20] open("/dev/random", O_RDONLY) = 12 <0.000202>
    ...
    444   07:46:10.114873 [00007f72c2ec3de0] poll([{fd=12, events=POLLIN}], 1, 4294967295) = 1 ([{fd=12, revents=POLLIN}]) <1213.468633>
    444   08:06:23.583578 [00007f72c38af4e0] close(12) = 0 <0.000018>

The cryptography python package is installed as a dependency of docker[ssh] 3.7.3.
So I installed cryptography 2.7 package on the RHEL7.3 server that is not installed docker python package.
But the problem was not occured this's why I wonderd the problem cause is docker[ssh] 3.7.3.

I don't detect this issue on CentOS.

My system/test specs:

• Python: 2.7.5
• docker with ssh install option: 3.7.3
• cryptography: 2.7
• pip: 19.1.1
• OS: RHEL7.3

The report names docker-compose 1.24.0, docker[ssh] 3.7.3, cryptography 2.7, Python 2.7.5, and RHEL7.3, but no repository file or test. Start by reproducing the delayed boot with the listed dependency combinations and inspect the supplied strace; done would require a confirmed cause and a reproducible solution or documented incompatibility.