this is what I did already. But nevermind either I didn't have my eyes in front of my sockets or something cause I' can't reproduce the issue now for some reason even though the file has uppercase it's all in lowercase in the conflict panel
ok I dunno what I did wrong but I cleared the overwrite folder of asis work remnants (log files and a lot more) and it's working. so I guess it was an asis issue from the start or maybe it's because of MO that some files were left over (because previously when I used NMM and ASIS ever failed, it didn't leave that much files behind it as far as I remember) and a single failure will hence cause subsequent failures
now I'll just have to find the problematic mod and to not forget to delete the overwrite folder contents xD
thanks for all the help, without you I wouldn't have been able to find this that quick.