Create Sparklines very slow when lots of Sparkline Groups already existed for given launch

Hello,

I have an Excel file that I use for some personal projects for which I could really please use some help. The macro will create or delete non-contiguous sparklines; only one worksheet would ever have Sparklines and no other charts are present in the workbook. The data for the sparklines is kept on a different sheet then the sparklines. The quantity of sparklines will vary depending on source data and can be upwards of 10,000+.

If the xlsb file is launched when no sparklines are exist, then the code to create the sparklines runs upwards of 10 to 30 times faster than if the sparklines had previously existed for a given launch of the file. Removing the sparklines or deleting and recreating the entire Target sheet does not improve the speed, only saving without Sparklines and relaunching.

The slow performance can have a major impact. For example: ~8,000 Sparklines takes ~55 seconds to execute when running quickly but can take ~1700 seconds if Sparklines were either already present when the file was launched or had previously been created and then removed. Smaller sets of Sparklines would naturally take less time to create but would still suffer from the same difference in the speed at which they are created, i.e. a smaller set of Sparklines might take 1.5 and 20 seconds to execute for the fast and slow executions respectively.

Sparklines are placed into cells that previously contained numerical results, and the results are Backuped up on a different worksheet as they would be replaced when Sparklines are removed. There are no formulas or conditional formatting in the workbook.

ToggleSparklines function is triggered from the Target sheet via a button so the Target sheet is active at the time the function is triggered.

I have spent hrs and hrs trying to figure out this problem, and I have exhausted everything I can think to try. This is my first time submitting a thread so hopefully I am doing it correctly.

I would really appreciate any possible suggestions. Thank you very much

NOTE: the sample code has been removed since the code contained in subsequent posts is targeted more at the specific issue.