Unfortunately this workaround does not fully solve our issues.

It does solve the immediate problem of wronlgy placing the buttons outside the visible field for the case outlined above. Using the SequenceBox, the buttons are equally spaced instead (which is not the behaviour we saw in SWT where the buttons were right aligned with no additional whitespace between them). However, we've managed to fiddle around with some config values to mimick the SWT behaviour. In essence the same fiddling also allowed us to mimick the behaviour using GroupBoxes, so changing from GroupBox to SequenceBox *does not* completely solve the spacing issue, it just converts it from "spacing outside visible gui" to "equidistant spacing".

However, a greater issue is a case where we are using different width fields. Using a GroupBox we were able to nicely space elements, but using the SequenceBox I have not been able to mimick this behaviour (even in Mars).

Another issue seems to be that we are able to change the font colour of the second field from black (initial value) to red, but any attempt at changing the colour back from red to black has no effect.

I am attaching a screenshot of what our current Mars based SWT GUI looks like and what our best effort in Neon has achieved.

• I need to fiddle with various getConfiguredXxxx() properties in different ways between Mars and Neon to reproduce the same look and feel. When doing that, I can also get GroupBoxes to look very similar (a bit of spill on the right hand side, overlapping the last button with the scroll bar), so the SequenceBox is marginally better than the GroupBox but does not really avoid the issue that manual migration effort is needed to tweak the properties.
  
• in a GroupBox we can mix various fields some, with configuredGridW > 1 and this looks quite nice (see the screenshot), changing the GroupBox to a SequenceBox leads to a totally broken layout. (also visible in the screenshot).
  Is there a recommended way to vary field widths of fields within a sequence box? It seems configuredGridW is not the way to go...
  

• The default of gridUseUiWidth was changed from true to false for buttons. That is why you had the space between the buttons. I updated the migraton guide accordingly: http://eclipsescout.github.io/6.0/migration-guide.html#button.
  
• The groupbox uses a gridW of FULL_WIDTH by default, compared to the sequencebox which uses a gridW of 1, like a regular form field. That is why you need so set the gridW manually if you use a sequence box.