Probably there’s a wrong expression map for the trumpet sample loaded and it is trying to play a keyswitch to trigger a certain articulation that happens to be the note Eb.
Often VST instruments use special notes outside of their normal playing range to change articulations (ex. between legato, staccato, trills, etc) - these are called key switches. If the expression map for the wrong instrument were mapped, the keyswitch it is trying to play might actually fall within the sounding range of the instrument and then you’d hear that note as though it was stuck.