Hello Heizi,
We have the same problem after upgrading to 2.3.8 - the slave wasn't updated and is still version 2.3.2. We tried upgrading the slave using the site available at http://[ip]/2/ (and also by creating an SSH tunnel to the master and using the slave's Target IP), but even after it says that the upgrade is completed, it stays at 2.3.2. Is there anything we can do?
Sorry for the trouble. Could you give me remote access for a check? Teamviewer is ok.
For convenient contact, you can add my skype: This email address is being protected from spambots. You need JavaScript enabled to view it.
BTW, We are on holidays from February 10th – 21st, 2018 in observance of Chinese New Year. And get back office on February 22nd, 2018.
Between that time, maybe i can't reply your message ASAP. But when i am available, i will help you to check it.