Didn't catch when exactly you got back on reta. Under a month back and you're still climbing the titration curve. That opening 8mg dose following a long pause only lifts your system to about 8mg. Once a full month at that weekly amount passes, the same injection ends up carrying your body closer to double that, roughly speaking. So during that entire opening stretch after restarting, you've genuinely been sitting at a lighter internal amount than you had before stopping.
Much of the extra weight that showed up during your break was probably swelling tied to inflammation rather than genuine fat gain. Getting back on reta likely flushed that retained fluid quickly, there's no realistic way that many pounds of actual fat vanished that fast. While your body's still sorting itself out from that swing, the number on the scale isn't a reliable stand-in for fat levels right now.
During your original run on reta, that early water-driven stall probably never showed up because fat was melting away fast enough to completely bury any minor rebound in fluid that would've followed. This time your rate of losing fat