I'm developing an application using Qt's Modbus RTU Serial Master implementation, and I'm encountering several issues:

1. I'm getting an ASSERT failure in the processQueue function:

   ASSERT failure in processQueue: "response timer active", file c:\users\qt\work\qt\qtserialbus\src\serialbus\qmodbusrtuserialmaster_p.h, line 302
   

2. I'm seeing messages about incomplete ADU reception:

   qt.modbus: (RTU client) Incomplete ADU received, ignoring
   

3. Occasionally, I get a send failure message:

   qt.modbus: (RTU client) Send failed: 0x0300000024
   

4. There's also a message about not being able to calculate PDU size:

   qt.modbus: (RTU client) Cannot calculate PDU size for function code: 18 , delaying pending frame
   

My questions are:

1. What could be causing the ASSERT failure, and how can I resolve it?
2. How can I improve the reliability of the Modbus communication to avoid incomplete ADUs and send failures?
3. Is the PDU size calculation issue related to the other problems, and how should I address it?
4. Are there any known issues with Qt's Modbus implementation that could be causing these problems?

I'm using Qt version 5.12.12 on WINDOWS.

Any insights or suggestions would be greatly appreciated. Thank you!