Can very natural biological shifts play tricks on the scale on a day-to-day basis?
In a nutshell, yes. Us girls know this very well thanks to our hormones but there are a lot of factors that affect the scale. If you do a hard workout, the next day you'll have some swollen muscle tissue at the molecular level while the tissue rebuilds itself. Swelling = water weight gain. This will show up on the scale even though it doesn't in the mirror. Sodium, alcohol, and caffeine can all affect your hydration status as well. Since we are mostly water, small fluctuations in hydration can have large impacts on the scale. A high fiber meal will retain water as it passes through your digestive tract (one way fiber prevents constipation) so even healthy low calorie foods can affect the scale. FWIW I also weigh daily but I only record it weekly. I can't slip too much in a week, and it helps to even out those pesky data points.
Your scale may move down slower at a smaller deficit, but if you truly are at a deficit, it will still move down over time. If the scale doesn't reflect what the log says, then you need to reevaluate the accuracy of your activities and the way you measure your portions.
I won't comment on the workouts, men are built differently so what works for me won't work for you on that front. But I do agree on the protein. Your body needs protein to produce the many day to day hormones that keep everything working. If there's insufficient protein in the diet to maintain hormone production, the body will take protein from muscle tissue to keep these vital functions going. Excess protein will be turned into fuel, so as long as you're in good health, it's very hard to eat too much protein.
If I keep starting over, eventually it will stick, right?
Current weight: 140
Goal weight: 135