You will need to provide more information; otherwise you can expect to get a handful of guesses or limited responses. Please show the dynamic content you are using in your action. What is the trigger? Show the part of the flow that contains the Get Attachment action.
Here's my first recommendation: If you are using the trigger When a New Email Arrives (V3), I rarely use Get Attachments anymore because you can set the 'Include Attachments' to Yes in the trigger (and 'Only with Attachments'); you don't need Get Attachments if that's the trigger.
Here's my best guess though: don't resubmit a failed or successful run. Send an email or do whatever the trigger needs to start a new flow run; often times resubmitted runs will not find the attachment data. So if you are using the trigger When a new email arrives (V3), submit a new email; not a resubmitted run.
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