Exported audio has 1 frame without sound

I have this big project with numerous files and sequences, and the sequences that go to render comprise nest-blocks (green). They are all placed together with no gaps, below is an mp3 music file cut in the parts where nests meet so every nest is exported with the corresponding part of the music (yellow). 

So, I am to export these blocks individually one by one using in and out points. I double-checked it - the markers are placed exactly in the cuts between the blocks - i do it with X hotkey. But in the end the exported videos all have 1 frame with no sound while retaining the full video:

So when the clips are brought back to Premiere and placed next to each other you can clearly hear this 1 frame with no sound.

Why does it happen and how to correct it? I NEED A SOLUTION ASAP!

• All the nests were created inside the sequences out of groups of media on the timeline. There was no gaps, the sound met the ends of all the clips. 
• All nests and sequences are 25 fps. If I export the nests contents separately there’s no issue
• All tracks have Premiere own audio effects on them. Removing those does not cure the issue
• Clearing the cache does not solve the problem either

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