How do I merge in batches?
Available only in the Google Docs Add-on
If you have 100s of rows to merge it is best if you batch your merges as Google services may not be able to handle the load at once and it will start issuing errors (such as NetworkError: Connection failure due to HTTP -1).
It may be best to merge by 50 or 80 rows depending on how heavy your document template is.
You can apply batching by clicking the Options link and set the following fields:
1. Track Merge Row: Create a column in your sheet and call it 'Merged'. Assign it to this field. This will allow the add-on to track which rows have been already merged.
2. Batch Size: Indicate how many rows you want to merge at one go.