World's worst water retention?

Very low calories can increase water retention (potentially in a creeping manner, adding to quite a total) via cortisol, and reduce daily life calorie expenditure (perhaps subtly, but meaningfully) through fatigue.

I started losing weight around your size, 5'5", 183 pounds, age 59, and lost well, joining MFP at around the mid-150s, and lost all the way to goal in mid 120s pretty expediently, eating 1400-1600 plus all carefully-estimated exercise calories (something you have quite a few of, and you're just using them to increase your calorie deficit from probably high, to extremely high). So, I was eating 1600-2000+ gross calories most days. I admit I'm a mysteriously good li'l ol' calorie burner for unclear reasons, but I still think it would make more sense for you to increase calories rather than decrease them, at least for a month or so trial period.

At your age and with the exercise, we'd expect your TDEE (total daily energy expenditure, i.e., all day all source calorie burn) to be around 2000-2200 or so. You're eating 1300, doing conservatively a couple of hundred calories of exercise, so netting out around 1100 calories. In theory that would result in over two pounds a week loss, but at about your same size, 2 pounds a week was dysfunctionally fast for me (I eventually got weak and fatigued, rather than retaining water, but . . . . ).

I'd suggest you go through at least one full menstrual cycle eating either TDEE - 20%, or your MFP goal (with activity level set based on life before exercising) plus a reasonable estimate of exercise calories.

If you increase calories, you'll see a scale jump initially, virtually right away, from effects of the added food, but it's water & digestive contents on their way to becoming waste, not fat, so don't let it dissuade you. It will take some time for the water part of it to balance out - particularly if you're retaining some already - but stick with it for one, maybe 2 menstrual cycles, see where you are.

I did look at your diary (thank you for having it open, that helps). Nothing jumps out at me as a major potential source of logging error as long as everything is there as you indicate, but if your MFP goal based on profile settings (per MFP instructions) is 1390, and your synched Fitbit is adding calories . . . you should eat right around the total that results, not hundreds of calories below that number.

I'm guessing you probably told MFP you wanted to lose 2 pounds a week (aggressive), and that would already be built into your goal calories. When you synch your Fitbit, MFP takes Fitbit's numbers and reconciles them to keep you at the same estimated loss rate. You shouldn't be eating consistently below the goal calories that results, that's just increasing your physical stress level (potential for water retention, among other things) plus increasing health risk, not to mention probably making compliance harder and burnout more likely.

It wouldn't hurt to drop the loss rate target to 1.5 pounds a week, even.

Eat to your goal, or close, like +/- 50 calories or thereabouts. For at least one, maybe two monthly cycles.

I'm very similar stats to you and had a very similar experience to yourself seeing no difference in the first few months. I was getting very disheartened. Was logging from Sept to Dec last year but on a different app but going back over my records my diet was identical to what I'm eating now. The main difference for me was upping my active steps and increasing intensity of deliberate exercise. I lost approx 30lbs from Jan to June this year and it was the increased activity that seemed to kick it off. I also went lower on carbs and higher on protein. Feel free to friend request and have a look through my diary. I've been less consistent with logging the past few weeks as I'm trying to maintain at the moment and be less reliant of tracking everything.

When I look at your weight chart, I see an overall downward trend. I think you need to give it more time.
Good luck.