The fact is a lot change can mess you up, not just a primer substitution, but it is more likely with a powder than a primer in my experience.
I am glad the OP found his primer again. But with the break up of Remington I would try to source more if the opportunity affords itself, just because.
I would also test for an alternative brand of primer so you have a “fall back” load in the wings. It may even require a different powder.
I had a fly shoot’in load in a .22-250 Rem 788 that took me forever to find. It involved WW 760 powder. I told a long in the tooth gun enthusiast about it. He told me I had better go and source that lot of powder like there was no tomorrow.
I had experienced a lot change already and no determental effects so I reflexively laughed ...... he got mad and set me straight!
His anger with me got me motivated and caused me to find just one remaining powder in stock of that lot. When I ran out of that pound I bought the next lot number and it was all washed up!
I tried and tested until I was blue in the face and to no avail, primers, powders everything but my .460” for five shots load was no more! I finally settled on Varget and .6” but more velocity.
You know what? Coyotes died just as well if not better with the added velocity!!
It comes down to what you are doing with your ammo, expectations are one thing. Needs are sometimes another.
Three44s