LaL audiences sometimes don't pair well with VO campaigns: VO campaigns require a very wide "surface area" of potential users in which to explore. The way VO works if it's not min-ROAS constrained is that it just bids whatever it needs to in the auction to acquire what it deems to be the "highest value" users; it's entirely possible that the bid used might not back out to a positive Day-X ROAS for you.
I'd suggest some combination of:
- Using a min-ROAS setting to ensure that ROAS falls within your standard (note that if you are currently not meeting that standard without min-ROAS, then setting the min-ROAS value will likely just decrease delivery);
- Increase the scope of your LaL audience with either a significantly larger seed audience or a significantly larger LaL percentage;
- Don't target a LaL audience and give VO the loosest possible (eg. Tier 1 countries) audience targeting parameters in which to explore.
More thoughts on this: