I for sure have felt the same with the whole "themes" idea. It why I stopped doing rated puzzles because I feel like my rating or learning wasn't that representative/beneficial! You definitely are not the only one, I feel like its the luck of the draw.
Are the rated puzzles randomly selected or come in "waves" of themes?
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I am hoping to hear if anyone has noticed whether the puzzles that are presented to you in rated puzzle mode (not puzzle rush, etc.) comes in sets of certain themes or are they completely random? I am seeing a pattern in my performance where I will in regular intervals shoot up by 100-150 rating points, and then will come a week where I lose the same amount, I will be literally unable to figure out any puzzle (even ones 500 points under my rating) for several days, and then all of a sudden they seem so easy again and I gain again. All I have determined so far is that it is NOT a case of the puzzles getting easier when my rating drops because the puzzle ratings themselves are still the same (i.e. on a bad week I'll fail 5x 2100s in a row and on a good week I'll have 100% success against the same). So it isn't purely driven by puzzle difficulty.
Basically I'm trying to figure out if this is like "puzzle tilt" for me where I should simply take a break on those bad weeks and do nothing, or else if I'm just having trouble with certain themes, in which case instead I should study. I'm not aware of any feature on (free) chess.com where I can analyze whether I am bad in certain areas.