I was really scared of upping my calories, but i'm glad that I did! It has shown some pretty good results so far. Saw a little bit of a loss on the scale, some body fat% loss, just have inches left to lose now. Only been doing it for a week or so steady. It takes time.

Have you looked into the scooby calculator?

I'd still increase slowly, just not 100 slowly. Like 250 slowly each week.
2350 - 2600 - 2800

If your system is slow in speeding back up - no real need to add actual fat back on during the process during the time you are eating in excess of suppressed TDEE.

So if your activity level hasn't changed - you had about a 45% deficit prior eating at 1800. That's rather major.
But only 4 months? That's not too bad.

But frankly you can't suppress your system that much to NOT lose weight at all. You still should have been close to 1 lb weekly.

So you might investigate food logging being accurate, perhaps wiping out some of that deficit.
Also if you are manually logging exercise on Fitbit/MFP, how are you getting the calorie burns.
And does the distance the Fitbit says you walk correct, since that is ultimately what daily burn above BMR is estimated from.

You need to log your lifting for accuracy too then. No matter what model.

Inflated it would be.

HRM formula for calorie burn is ONLY valid for steady-state aerobic exercise, same HR for 2-4 min.
That is the only connection between HR and calorie burn, for the delivery of oxygen to sustain the effort of burning fat and carbs.

Lifting if done right is anaerobic and opposite of steady-state with HR going all over the place constantly, totally falsely elevated related to your level of effort, and false elevated calorie burn too.
Ever watched your HR for 1 min after a lift was stopped?
Is that really the HR required for standing there watching it?

Always manually log lifting.

Weights on Fitbit is based on studies of the traditional sets and rests of 2-4 min and reps 4 - 15.
Circuit Training is rests up to 1 min, reps 15-20, done in circuit style rather than sets.
Calisthenics is rests less than 1 min, reps 15 and usually over 20, usually body weight.

log it as exercise, and set your start time and duration

The HR-models if they don't see enough steps along with higher HR stop doing per second logging and calorie estimating based on HR, and back to step based calorie burn.
You might not have had enough steps, or the HR reading was inaccurate too, not reaching the actual highs or missing spans of time. Many find that compared to EKG accurate chest straps.

Did you see in HR stats if there were blank periods of no reading?

And it's true, manually logging a workout gives no steps or distance unless you are entering in running/walking workout.
But the steps/distance seen/calculated are kept, only calories is overwritten.

I'm surprised you got that many steps during lifting workout, unless pretty long and you walk around.
I get like maybe 1 step doing 15 squats for that time with Zip on my hip. Obviously a 1 step pace in 45 seconds is pretty low calorie burn.
Perhaps wrist mounted it saw the ups and downs better and counted them as step impacts.

So it depends on if it switched from HR-based to step-based calorie burn at some point. And if HR-based, was it accurate HR that was seen to base calorie burn on.