==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.6.1
- Deployed with iRedMail Easy or the downloadable installer? downloadable
- Linux/BSD distribution name and version: Ubuntu 16.04.6 LTS
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx): Nginx
- Manage mail accounts with iRedAdmin-Pro? YES
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

Hi, upgraded iRedAdmin-Pro to 5.3 (from 5.2)
And now I cannot access the admin page, just shows "Internal Server Error"

syslog trace shows below:
May  2 10:37:36 ip-172-31-1-83 iredadmin: Traceback (most recent call last):
May  2 10:37:36 ip-172-31-1-83 iredadmin:   File "/opt/www/iRedAdmin-Pro-SQL-5.3/iredadmin.py", line 8, in <module>
May  2 10:37:36 ip-172-31-1-83 iredadmin:     from libs import iredbase
May  2 10:37:36 ip-172-31-1-83 iredadmin:   File "/opt/www/iRedAdmin-Pro-SQL-5.3/libs/iredbase.py", line 5, in <module>
May  2 10:37:36 ip-172-31-1-83 iredadmin:     import web
May  2 10:37:36 ip-172-31-1-83 iredadmin:   File "/opt/www/iRedAdmin-Pro-SQL-5.3/web/__init__.py", line 4, in <module>
May  2 10:37:36 ip-172-31-1-83 iredadmin:     from . import (  # noqa: F401
May  2 10:37:36 ip-172-31-1-83 iredadmin:   File "/opt/www/iRedAdmin-Pro-SQL-5.3/web/db.py", line 757
May  2 10:37:36 ip-172-31-1-83 iredadmin:     f"{round(b - a, 2)} ({self.ctx.dbq_count}): {str(sql_query)}",
May  2 10:37:36 ip-172-31-1-83 iredadmin:                                                                 ^
May  2 10:37:36 ip-172-31-1-83 iredadmin: SyntaxError: invalid syntax
May  2 10:37:36 ip-172-31-1-83 iredadmin: unable to load app 0 (mountpoint='<expunged>|/iredadmin') (callable not found or import error)
May  2 10:37:36 ip-172-31-1-83 iredadmin: --- no python application found, check your startup logs for errors ---
May  2 10:37:36 ip-172-31-1-83 iredadmin: [211.193.16.6] GET /iredadmin 500 104 "-"

Any idea on how to fix this error?