I am not familiar with this particular bit of Wagner, but I listened to some of the YouTube versions, and as best as I can determine the problem is that the Brass measures have the correct number of notes but start on the wrong beats after the Violins change to 9/8, hence you have the three Brass notes but instead of having three more immediately, nothing happens for a few beats . . .
This is how I input the music notation in NOTION 4, and the first measure sounds a bit like some of the YouTube music videos . . .
Overture for Tannhaeuser (Wagner) ~ NOTION 4Measures and time signatures are a bit strange generally, and there are different perspectives on how everything should be handled, but I like the perspective of Joseph Schillinger's System of Musical Composition (SoMC), where the correct location of vertical bars or measure ending and beginning points occurs when the various rhythm pattern components all play a note at the same time, which depending on the rhythm pattern can map to a measure having several hundred or thousand beats, with this being the reason that I tend to do everything in the key of C and 4/4 time, because 4/4 is just as wrong as all the other time signatures . . .
Toward the goal of understanding the rhythm patterns in the SoMC, consider the rhythm pattern with three beats, one on 1; one on 3; and one on 5 . . .
Three people can do this on a table, and it is quite amusing at first, since everybody (formally trained or self-taught) gets confused at first and loses track of when they are supposed to tap . . .
The first person taps on every beat, and this is the person who is playing the "1" beat . . .
The second person taps on every third beat, which is the "3" beat . . .
And the third person taps on every fifth beat, which is the "5" beat . . .
The rule in the SoMC is that measures end when the three people all tap on the table at the same time, which as a greatest common divisor or whatever type of arithmetic computation puts the number of beats in a measure at 15, since the first person taps on every beat, but the second and third persons will tap on the same beat only every 15 beats, so if a quarter note gets one beat, the time signature is 4/15 . . .
If you are focused primarily on how the music sounds, then you might try using a time signature like 4/1000 so that there essentially are no measures . . .
This is all that comes to mind at the moment . . .
Lots of FUN! P. S. My focus is solely on the way the music plays and sounds, and NOTION rules on this, but if I had to prepare sheet music with elaborate music notation requirements, I would use Sibelius 7, since its primary focus is engraving and so forth . . .