Stellar-core is a reference implementation for the peer-to-peer agent that manages the Stellar network. Prior to 20.4.0, core nodes could be randomly crashed due to a race condition with a 3rd party library. The likelihood of affecting the network is low since crashed nodes come back up online right away. Code fix mitigation is part of Stellar-core v20.4.0 release
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.