I've tracked down the issue.
 
The short story is that the "Type" workaround is never called on the C4 for a default ProChannel setup, and it's down to the following:
 
Selecting "EQ" from the C4 always brings up the 1st ProChannel plugin regardless of whether it's a type of EQ or not. So for a default ProChannel setup, pressing "EQ" always brings up the Track Compressor.
 
However, scrolling through the list of plugins does only show other EQ plugins.
 
A similar thing happens with dynamics, in that the "Dynamics" button always brings up the 2nd ProChannel plugin regardless of its type, but scrolling through any other plugins in the list only shows Dynamics plugins. For a default ProChannel setup, pressing "Dynamics" always brings up the EQ.
 
The Type workaround checks to see if it's the "Type" parameter, but also if filter type is "Dynamics" - however on the C4, you have to either select "Plugin" or "EQ" to get to the Track Compressor if it's the first ProChannel plugin. So the filter type is never dynamics for a default ProChannel setup, and the workaround code never gets called.
 
So half of the fix would be to sort out the EQ & Dynamics buttons and make sure they're checking the ProChannel plugin type before selecting it. This would ensure the type workaround gets called... however if you navigate to the Track Compressor using the "Plugin" button, the workaround code still wont get called.
 
A safer fix (the 2nd half of the fix) might be to set a flag somewhere to say the current plugin is actually the Track Compressor (maybe by checking it's name - as it has to send this to the plugin anyhow, or it's VST identifier if that's available), and check this flag in the Type workaround instead of the filter type.
 
For the moment though, removing "Type" from MackieControl.ini stops the crash from happening.
 

It is good to know my mod is not working for C4. Well, it was not designed for it since I was unable to test.
 
The complexity of finding ProChannel modules is the following (I have written that before):
1) the name for ProChannel modules is not returned, so that can not be used to identify them
2) for current strip, all modules can be accessed, in the sequence they are in the ProChannel. There is special call to find where are EQ and Comp in this case.
3) for other strips, only EQ and Comp can be accessed. The order depends from the order in the current strip.
 
So, broken since the introduction of ProChannel...

I've got a fix - just tidying it up and doing a bit more testing before I commit.
 
The EQ / Dynamics button issue is to do with the host name changing from "SONAR" to "Cakewalk". This meant that the flexible ProChannel flag was always false, and hence it didn't "look" for the correct class of plugin. Adding in another clause for "Cakewalk" fixes this.
 
I've also improved the "Type" workaround by setting a "current plugin is track compressor" flag when it retrieves the plugin information. This is passed down during the binding to the MixParam class and is checked instead of the plugin filter type. This makes the workaround safe when using the "Plugin" button as well as the "Dynamics" button.
 
I'll let you know once it's committed to GitHub and point you to the location so you can merge the changes in to your branch.

@Noel / Alexey - The latest code is now available here:
 
https://github.com/msmcle...k-Control-Surface-SDK/
 
Apologies for splitting this up into two commits, I forgot to update the binaries on the first commit.
 
Everyone else... if you want the latest MackieControl.dll you can get it here:
 
https://github.com/msmcleod/Cakewalk-Control-Surface-SDK/blob/master/Bin/x64/MackieControl.dll
 
Note that until these code changes are integrated into the main Cakewalk repository, this will get overwritten on every CbB upgrade. Until then, you'll need to manually replace it after each upgrade.