System.InvalidOperationException: "Die LinkedList ist leer"

[Stiwa-PohG]

Reason
This error occurs when reading variables. A variable is read every second. Everything works fine at first, but after a certain amount of time (a few hours) this error occurs.

Question
Doesn't this linked list need to be thread-safe, or how could a concurrent change to the list occur (race conditions)?

StackTrace:
S7CommPlusDriver.dll!OpenSsl.OpenSSLConnector.GetNextBuffer(System.Collections.Generic.LinkedList<OpenSsl.OpenSSLConnector.DataBuffer> list) Line 333 C#
S7CommPlusDriver.dll!OpenSsl.OpenSSLConnector.PerformRead() Line 245 C#
S7CommPlusDriver.dll!OpenSsl.OpenSSLConnector.RunSSL() Line 204 C#
S7CommPlusDriver.dll!OpenSsl.OpenSSLConnector.ReadCompleted(byte[] pData, int dataLen) Line 234 C#
S7CommPlusDriver.dll!S7CommPlusDriver.S7Client.RunThread() Line 182 C#

Exception