Cluster is split in 2-3 locations on tsne plot - Suerat
Your cluster labels come from graph clustering implemented in the FindClusters() function. The resulting clusters are then visualised with a 2D tSNE plot (via RunTSNE() and TSNEPlot()). So, your cluster 13 is not split into three sub-clusters but cells within cluster 13 look somewhat distant from each other on the tSNE plot. Having mentioned distances on a tSNE plot, please see this SE Data Science entry Can closer points be considered more similar in T-SNE visualization? and especially the comment "What I mean is that you can't just use distance in the lower space as a similarity criterion". In your case "the lower space" would be your tSNE plot.

As far as I can see from your code, you are following the widely-adopted "Seurat workflow" and all seem fine including your TSNE plot output. I could not spot the QC step though: apart from the one at object initiation, one usually applies filters for number of genes and % mitochondrial gene contribution (using FilterCells() in Seurat v2 and subset() in Seurat v3).

It would be a good idea to try UMAP instead of tSNE, please see Evaluation of UMAP as an alternative to t-SNE for single-cell data (Becht et al, 2019). Seurat v3 vignettes are now using UMAP and not tSNE any more.

Lastly, please see How to Use t-SNE Effectively to learn about points to take into account when using/interpreting tSNE plots. You will see that you would get surprisingly dissimilar tSNE plots from the same underlying data with different parameters (some are hardcoded in the RunTSNE() function).