Title says it all.. I combined a set of polygons on the first instance of Geometry generator using something like this:

    buffer(buffer(collect( $geometry, concat("MZNA","REGLABEL")), 0.1), -0.1) 

Buffers are meant to join poligons with a little separation. Thing is, after that I defined marker lines to simulate measurement, but in the case of multipart polygons, I get random measures floating between the different 'islands'. So I want to separate them before measuring, but I dont know how...


EDIT:
[![What im trying to avoid is this:][1]][1]


  [1]: https://i.sstatic.net/Eo53a.jpg

Im using the approach shownin https://gis.stackexchange.com/questions/165574/qgis-how-to-label-individual-sides-of-polygon/314789#314789 by @she_weeds. My problem is, as shown in the pic, after collecting and buffering, I get some multipolygons and those ones gets an extra text floating between the polygon parts. Is there a way to avoid it without dissolving the generated geometry? 
Im not experienced enough to know if its possible to test each line, for example