The Logic App is transferring files before the source has finished loading them

we understand that the Logic App trigger fires as it detects a new file in the on-premises file system. However, it does not verify whether the file is fully written or still being transferred. This leads to incomplete files being picked up and sent to the destination.

Logic App triggers such as “When a file is added or modified” are designed to respond immediately to file system changes. They do not natively check for file completeness or lock status before initiating the workflow

Use a naming convention or temporary file extension during file transfer,

Write files with a .tmp extension.

Rename to .csv, .xml, etc., only when the transfer is complete.

Configure the Logic App trigger to ignore .tmp files and only act on finalized extensions.

This approach is widely used to prevent premature processing.

Implement a pre-check using a script or Azure Function,

Monitor the file size at intervals.

Trigger Logic App when the file size remains unchanged for a set duration (i.e., 30 sec)

This method avoids hardcoded delays and adapts to file size variability.

Use a hybrid approach,

A PowerShell or Python script runs on-premises to detect file completion. Once verified, it calls an HTTP endpoint to trigger the Logic App manually.

This decouples the trigger from the file system and gives you full control.

If feasible, move the file to an Azure File Share or Blob Storage after completion.

Use the “When a blob is added or modified” trigger.

This trigger is more reliable and can be configured to avoid partial file reads.

I hope this helps in resolving the issue, do let me know if you have any further questions on this