We are aware of a critical issue with NBXplorer being unable to process specially crafted transaction in the Bitcoin blockchain block 896727.
Our team has already deployed a fix. To resolve the issue with your BTCPay, update your NBXplorer to version 2.5.26.
If you're on the 2.x branch of BTCPay Server using btcpayserver-docker, simply click Update button in Server administration (or run http://btcpay-update.sh) and the issue will be resolved.
If you're on a pre-2.0 version and aren't ready to move to 2.x yet, you can switch to the 1.13.x branch and use it to bump the NBXplorer dependency. 
Thanks to everyone who reported the issue and allowed us to quickly deploy a fix.
For more details, please visit GitHub and review @Nicolas Dorier PR: 
If you're on the 2.x branch of BTCPay Server using btcpayserver-docker, simply click Update button in Server administration (or run http://btcpay-update.sh) and the issue will be resolved.
If you're on a pre-2.0 version and aren't ready to move to 2.x yet, you can switch to the 1.13.x branch and use it to bump the NBXplorer dependency. GitHub
GitHub - btcpayserver/btcpayserver-docker at 1.13.x
Docker resources for hosting BTCPayServer easily. Contribute to btcpayserver/btcpayserver-docker development by creating an account on GitHub.
GitHub
Fix improper parsing of transaction with some nVersion by NicolasDorier · Pull Request #1269 · MetacoSA/NBitcoin
The coinbase transaction 889d4fed1ec4a775d02082b5ff727f48d93013469db709d8d435e15b173118f3 wasn't properly parsed by NBitcoin, resulting in code...
