Problem with NET::ERR_CERT_DATE_INVALID and can't be accessed normally

Technical Details

Forum version : #phpBB3
Position : Administrator
Concerned browser(s) : Mozilla Firefox, Google Chrome, Safari
Who the problem concerns : All members
When the problem appeared : 15-Sep-2020 between 12:00 and 18:00 EEST
Forum link : ( link is hidden, you must reply to see )

Description of problem

My forum has some issues with certificate. And get error when you try to access it.
It was moved to https earlier this year and had no problems till now - loading properly with https.

1.First error without cookies cleared:
This site can’t be reached The web page at -my site url- might be temporarily down or it may have moved permanently to a new web address.
ERR_FAILED

2. After clearing cookies (Google chrome):
Your connection is not private
Attackers might be trying to steal your information from -my site url- (for example, passwords, messages or credit cards). Learn more
NET::ERR_CERT_DATE_INVALID

Subject: *.aforumfree.com
Issuer: Let's Encrypt Authority X3
Expires on: 15 Sep 2020
Current date: 15 Sep 2020

3. After clearing cookies on Firefox:
Secure Connection Failed message + PR_END_OF_FILE_ERROR error

Type: phpbb 3

Settings:
The internet address of your forum is currently: https:// + my site url
The SSL certificate for your forum is active .
Forum protocol : HTTPS (Secured) HTTP
Forcing HTTPS compatibility ("Secure" label) : Yes

Hello,

This issue is a server side issue. Our team is already aware and working on the problem.

For more information, or to report further issues related to this, please see the only topic: https://help.forumotion.com/t159527-only-topicunable-to-get-in-the-forums-ssl-error#1111940

Thanks and we apologize for the inconvenience.

-Brandon

Topic locked