Hello,

I have had a variegated monstera plant for a year and had no problems in that. In the last 1-2 months each leaf has developed brown spots. I thought this may have been sun burn but it's not in direct sunlight and the patches seam to be worsening and now leaves are turning yellow and I lost one last week and another this morning? but it has also put out a new leaf in the last week too. Im not sure how to rescue her. Any ideas from someone more experienced?

How close to a window is it?
Does it have any supplemental light?
How often do you check the moisture?
Does water come out the bottom when you water?
Have you fed it? If so, what with?

The brown patches in the places with sectorial variegation (variegation where there's largely a big patch of white) are normal. These patches have no chlorophyll, and will start to break down before any green parts or heavily variegated parts of a leaf will.
Many people try to 'stabilize the white' by using Cal-mag supplemental fertilizer and silicon. It doesn't really work. The sectorial variegation is just always going to brown and deteriorate.
I can't tell where the petioles of your leaves are...the leaf that is yellowing, is that an old leaf? Were the ones you lost older leaves?

Does the breakdown happen faster with less than ideal conditions? I was thinking that with brighter light the browning would be slower.

The browning and breakdown happens regardless. Only part of the leaf is photosynthesizing. This happens a lot more in Monstera deliciosa albo-variegata than it does in Monstera D Thai Constellation or one of the 'mints' because the variegation in the latter 2 is integrated. It occurs in splashes and smatters, not big sectorial patches, so the green is able to compensate better for the white. This is also why Thai C is a stable variegation, and is able to be tissue cultured, and why albo is unstable and can revert either to all green or all white, and has taken years and years to get to tissue culture, and still there are crop failures