PlentyShop LTS Frontend Error & SDK Validation Failure

I have been analyzing a PlentyShop LTS setup for testing purposes and encountered a couple of issues that seem to be related to the PlentyMarkets environment.

Firstly, the frontend store is currently not opening. The following error is displayed:
{„error“: {„message“: „IO\Extensions\Functions\ExternalContent::getExternalContent(): Return value must be of type array, null returned“,„code“: 0}}

Secondly, regarding our payment plugin:
We had previously tested and confirmed compatibility with PlentyShop LTS version 5.0.81, and everything was working as expected. However, without any changes from our side and with no visible updates in the shop, the plugin has suddenly become incompatible. During deployment, we are now encountering the following error: „SDK vendor validation fails“.

Why this happens?