Matrix Column Width keeps changing with different Filters

after some further tinkering, I realised that I still had the quarters as columns in the matrix, which was no longer needed, as I now want to show the data of only one quarter. after removing the field from the columns, it worked out as it should.
my interpretation is, that the columns for each value within a sector of a value defined to be used as columns really can be set to a fixed size, but that when changing the filter I was switching through different sectors (and ever only showing one at a time), which for themselves were having a fixed column width. The problem was just that I had multiple sectors, which I wasn´t realizing, and which caused the column widths to change whenever switching to another sector.
I hope this is comprehensible and helps somebody with the same niche problem!