Hello Peter,
I don't see any disagreement between us, just different wording/conclusion steps (or different understanding what KB3197954 could be).
Without having tested or confirmed it in any way I currently fully agree your conclusion, "KB3197954 released the problem" (others said the same). Based on this conclusion I went one step further and concluded KB3197954 must be an automatic update specifically
for Excel.
With "automatic update for Excel" I interpret KB3197954 interacted with Excel 2013 and according others also with Excel 2016, but KB3197954 did not interact in same way with Word 2013 or Windows 10, because the Windows 10 functionality "scroll inactive window"
is still working around Word ("scroll inactive window" just doesn't work any more around/for Excel be Excel the active or inactive window).
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As other people reported exactly the same negative/bad change we encountered the most important next step/feedback would be, can Microsoft see/confirm the problem, that around Excel 2013/2016 the Windows 10 functionality "scroll inactive window" is not working
in the most current update (after KB3197954).
{If to the contrary somebody would inform here that he has Windows 10 (automatically updated, this means KB3197954 installed) and around his Excel 2013/2016 the "scroll inactive window" is working we would be obliged to find other possible interaction reasons}