I'm working with this chart:

DateListPlot[{({{#[[1]]}, #[[2]]} & /@ revenues) /. 
   Rule -> List, ({{#[[1]]}, #[[2]]} & /@ profits) /. Rule -> List, 
  MapIndexed[{{revenues[[#2[[1]], 1]]}, #1} &, 
   Table[revenuemodel["BestFit"], {x, 1, Length[yearrange]}]], 
  MapIndexed[{{profits[[#2[[1]], 1]]}, #1} &, 
   Table[profitmodel["BestFit"], {x, 1, Length[yearrange]}]]}, 
 Joined -> {False, False, True, True}, 
 PlotLegends -> {"Revenue", "Profit"}, 
 FrameLabel -> {{"USD ($)", None}, {"Year", None}}, 
 PlotLabel -> "Revenue and Profit of " <> "IBM" <> " Over Time", 
 PlotTheme -> "Business"]

It makes a DateListPlot with unjoined datapoints for revenue and profit, and two joined lines for the linear model of each, like this:

All the variables are properly defined prior to evaluation.

However, when I put the same chart in a NotebookTemplate, with all the variables replaced with NotebookTemplateSlots, the second trendline isn't rendered:

Note, however, that there is a dot at the place where the trendline starts, and further investigation indicates that this is in fact a very short line, only at that point. As the chart renders properly outside of the template, I think this is most likely a bug. I will continue investigating, though. There might be a problem with my data.