It is very common that at some point your certificates expires and you need to renew your certificates. A common issues that I saw in projects is the following error:

The certificate was not found. Store: My, Location: LocalMachine, FindType: FindByThumbprint, FindValue: [YOUR-Thumprint-Value-Here], InvalidAllowed: False.
Source: Sitecore.Xdb.Common.Web

If you have a CM in one Server and CD server in another server. It is probably that you forgot to install the xconnect certificate in CD server.

You can run the following commands to validate if you have correctly installed the certificate for each server.

On CM Server run

Get-ChildItem  -Path Cert:\LocalMachine\MY | Where-Object {$_.Thumbprint -Match "[YOUR-Thumprint-Value-Here]"}

If you see a result then you can conclude that certificate is installed on CM server assuming that connect is installed in the same server.

Then you can check the same on CD server:

Get-ChildItem  -Path Cert:\LocalMachine\MY | Where-Object {$_.Thumbprint -Match "[YOUR-Thumprint-Value-Here]"}

If you noticed that you get no results, then you need to perform the following steps:

  1. Open Manage computer certificates in CM server.
  2. Go to Personal -> find the certificate that match your thumprint.
  3. Export Certificate

4. Move the file to the CD server

5. Install Certificate on Local Machine in Personal folder.

6. Grant Read access to the application app pool.

7. Recycle application pool and check your logs again.

Note: Be sure that thumbprint matches in CD server you can check the file ConnectionStrings.config to confirm that thumbprint is same as you certificate installed.

I hope that helps you to troubleshooting your certificates issues.