Issue Summary

If a user adds multiple attachments to a card simultaneously via API (or Power-Up/integration), the card's activity log will show activity for all attachments being added; the correct number of attachments will be displayed on the card front, but some attachments will be missing from the Attachments section of the card back.

Steps to Reproduce

1. Create a script to add multiple attachments to a card simultaneously
2. Run the script

Expected Results

All files added by the script will show under the Attachments section of the card back

Actual Results

Some of the files added by the script will be missing from the Attachments section of the card back, despite Trello showing the correct (total) number of attachments on the card front (next to the paperclip icon)

Workaround

Add attachments manually via UI or add a delay on the script between adding each attachment