I’ve done a quick test series. Initially used the project I have been working on with VSL orchestral instruments and EWQL Symphonic Choirs. Starting playback at a point where all parts have a marked dynamic at the beginning of the bar or are not playing, there are no problems. Start one bar later and in a run of 10 repeating the same bar, around 1-4 times the playback is too loud. Short break and repeat. Every time the loud entries are in a different place in the sequence. As previously stated, dynamics correct at the next explicit score marking.
Then deleted most of the project (42’ long with 6 flows) except for 24 bars. Behaviour follows the same pattern. If some parts have a direct dynamic marking and others don’t only those which don’t are too loud. This indicates that there is not a direct correspondence between project length and frequency. On the other hand, in two different projects of different length and complexity using only EWQL SC (one runs under VE Pro, the other directly in Dorico), I cannot reproduce the behaviour at all and yet with the original project including VSL orchestra, the problem does occur with the choir and is very easily reproducible.
With chamber music such as string quartets (irrespective of library used), I don’t very often notice it but on the other hand, it’s usually apparent with orchestral works – particularly with the BBC SO it seems – though again it’s not library-specific and appears to be to mainly be related to the size of the ensemble rather than project duration.