I’ll be the first to admit that I could be wrong about all of the above, it’s just my 2 cents. I couldn’t lose weight and exercise. When I stopped exercising fat loss became as effortless. It works for lots of people. You may be different, but then again your stall coincided with the most exercise you’ve ever done (triathlon training).
Here is my reasoning as to why 1800kcal might not work, trusting your satiety signals is your best option, and that fixing your satiety signals is priority #1 if they’re not leading you towards your goal:
Hunger signals and satiety signals are hormonal. Keto helps normalize hormones, exercise can disrupt this. Eating a ketogenic diet to satiety is superior to SAD and CRaP (Calorie Restriction as Primary) in every conceivable way possible, but it is not exempt from the fundamental principles of hormonal regulation, energy balance, and fat loss. People gain weight on keto all the time. If you can’t trust your hunger signals you will be lost in Stall City without a compass. Exercise can and does distort hunger signals.
If you eat to satiety and your hunger signals lead you to eat 25kcal/day in excess of your TDEE (total daily energy expenditure) on your lifting and cardio days, you will not lose weight on those days. Period. Those are 4 of the seven days of the week. Welcome to Stall City, population you.
All debate about CICO aside (and I have absolutely no interest in sparking such a debate), if you have not measured your RMR (resting metabolic rate), you have absolutely no idea what your TDEE is (total daily energy expenditure). The online calculators will tell you your RMR +/-25%. Your RMR may be 1600, or 1200, or 2000.
The good news is that if you haven’t had an RMR test, you have absolutely no idea what your RMR is. The bad news is that if you have had an RMR test done, you still have absolutely no idea what your daily RMR is. This is funny, but unfortunately it is also true. My friend primal.peanut bought the same $4,000 indirect calorimeter that DexaFit uses (Korr Metacheck) to track his RMR each day. I bought the slightly more sophisticated Korr CardioCoach CO2. His MetaCheck is newly calibrated, and certified to +/-3%. Here is his recent chart from a project that he and I are working on together. Note that his RMR (blue dots) ranges from 1800kcal/day to 2400kcal/day. It can move 400kcal in a single day. This is not his TDEE, this is his RMR! His TDEE routinely moves by more than double that amount.

Long story short, knowing that you eat 1800kcal/day simply won’t get you very far. You don’t know actually know your daily caloric needs. Even having an RMR test on a calibrated machine won’t fix that. If you can’t trust your hunger signals, you are lost in stall city without a compass. Exercise can and does distort hunger signals. There is a good chance that if you stop exercising, your hunger signals will guide you back towards slow and gradual weight loss.
I wish you the very best of luck, I know how frustrating a stall can be, especially when you are working so hard! I hope you find the culprit. It could be many things, but exercise-induced satiety signal disruption seems like the logical culprit to me based on what you’ve described.