That server is sending the 'short chain' which is not compatible with older Android clients. What version of Android are you using on the remaining system with a problem?
The 'short chain' is not the default chain from Let's Encrypt so you must have chosen that for some purpose. Here is more background on the long and short chains. This forum site for example uses the long chain.
UPDATE: @hassanjf Oh, I just realized your server is IIS. That chooses your chain for you. Still, the above applies and what version of Android is causing a problem?