Unfortunately I haven't seen any empirical data on the topic of freezing reconstituted peptides prior to use, so I don't want to endorse it in any way. I say just be safe and keep them refrigerated, not frozen.
While all feedback is welcome and appreciated, I think you might be overlooking something here. If you stopped GLP-1s 4 weeks ago and resumed them 1 week ago, they weren't out of your system and certainly you wouldn't anticipate resensitization. Retatrutide has a half-life of ~6 days. As a broad rule you shouldn't expect a drug to have cleared your system for 5 half-lives (30 days). And that's only for the drug to be out of your system, that says nothing about becoming resensitized to it.
I don't think a "bad vial" is the most likely conclusion here. More likely you're still just an experienced GLP-1 user going from physiologically the strongest (Retatrutide) back down to the introductory GLP-1 at a pretty moderate dose. That said, let me know how your next vial goes.