This sounds a lot like the other Chrome related issue you described here:
If the workbook causes high latency in Chrome for some reason, it could lead to such an issue. The way how "Paste Custom Text" works is by putting some content onto the clipboard, then sending cmd+v and then restoring the previous clipboard content again. If Chrome takes too long, BTT could already have restored the previous clipboard content again.
You can try to increase the time before BTT restores the clipboard contents. This command would set the restoration timeout to 1 second:
osascript -e 'tell application "BetterTouchTool" to set_user_defaults key "BTTPasteClipboardRestoreDelay" numberValue 1.0'