Normally, the Windows clipboard holds one item at a time. When you copy something new, it replaces the previous content.
However, if you place two Set To Clipboard activities back-to-back in the same workflow without any delay, UiPath may queue the operations and concatenate the strings before committing them to the clipboard. This is likely due to how UiPath batches clipboard operations in memory before the final flush.
There is high chance that it can miss to concatenate all the strings you are trying because it is suppose to overwrite existing data in the clipboard. It’s better to concatenate the string in a variable and then use Set To Clipboard activity.