With LFO1 set to “once”, the waves “saw” and “square” always reset to the start value after one cycle, making it very unuseable as an envelope, though it is presented that way in the manual. Random wave generation does not work correctly on key trigger as well. Those issues make the whole point of once mode a bit redundant.
All other synths featuring a one shot LFO (Nord series for example) don’t reset after one cylcle and therefore allow it to act properly as an envelope. This bug is now confirmed by UDO and I wonder why it has not been brought up before. I hope it will be fixed in the next update.