Why does the communication with a Siemens TIA PLC with TIA 20 and firmware 4.0 fail under specific circumcstances?

Why does the communication with a Siemens TIA PLC with TIA 20 and firmware 4.0 fail under specific circumcstances?

The communication using the S7TIA driver with Siemens TIA PLCs with TIA portal version 20 and firmware version 4.0 may fail under specific circumstances when combinations of variables are read.

This issue has been addressed by Siemens from firmware version 4.04 and requires an update of the Siemens PLC firmware.