EDL bug .. weird

I’m editing the sound on a movie.
i imported the movie to nuendo 29.97fps and the EDLs from premiere.
All works.
i save my works under different names “edit 01; edit 02; edit03 etc”
suddenly… i realise all the EDL markers are wrong… i don’t know when that happened but all the markers from the EDL that were ok at the begining don’t match. Another marker track i did manually by “scenes” matching the markers from the EDL is still ok. just the markers created from the EDL import are “buged” this way : TC00 is ok but the more i go in the movie markers loose 1 frame… 2 frames etc at the end of the movie (1h) all markers are off by 1 or 2 seconds (!!)
if i import that EDL again in my session i also have that “bug” BUT, if i “import tracks from Project” and select that same marker track but from first “save” i did and markers are ok.
what the hell happened ?
marker track is time based… i really don’t understand.
at one point i tried the “reconform” function with 2 EDLS (because film changed) and it didn’t work. Nuendo said :
can’t import the EDL as.edl do not match the current project frame rate… what ?
frame rate has never changed , film is 29.97 nuendo is 29.97 set using the “grab from video” finction.

anyone understand that ?

This sounds like drop frame/non-drop frame issues to me, although if that were the case it should be off by a little over 3 seconds after 1 hour; NDF vs DF is 108 frames an hour, or 00:00:03:18.

Was the EDL drop-frame or non-drop? Do all the timecodes in the 3rd/4th columns have ; or : separating them, or what does FCM: line of the EDL say (first few lines at the top)?