plotting – Why do the points in a curve are connected to those in another after FindClusters?

I have a few questions about the function FindClusters. There’s two group points data, and the following figures are obtained from these data.

Figure 1-1 is the the ListPlot of the first group, and Figure 1-2 is its ListLinePlot after FindClusters. Figure 1-1 tell us that the first group data can generate 5 smooth curves, but why Figure 1-2 present an unexpected result? Why do the points belonged to a line are connected to those in another curve?

Figure 2-1 shows that we can get 3 curves from the second group data. But, in Figure 2-2, the first two curves are joined to one curve. The distance between two points in the second curve is close, why don’t they joint together? The distance in the first two is far, but they are joined together. Why does it produce such a result? How to solve it?

Thank you very much.

Mathematica Version 12.3

Full Codes: Click here to download.
An excerpt of the codes:


(*figure 1-1, 1-2*)
trg=FindClusters(trData,5,Method-> "SpanningTree");

(*figure 2-1, 2-2*)
ListPlot(tiData, AspectRatio -> 5/7, ImageSize -> Medium)
tig = FindClusters(tiData, 5, Method -> "SpanningTree");
ListLinePlot(tiData, AspectRatio -> 5/7, ImageSize -> Medium)

Figure 1-1

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Figure 1-2

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Figure 2-1

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Figure 2-2

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