Hypothesis: if two crits happen at around same time, one of them can be "overlooked" in DeepWounds generation.
Hypothesis summary:
1. DeepWounds is affected by Trauma generated by the same crit hit but not affected by Enrage from the same source.
2. Buffs that are "on target" (Trauma, Blood Frenzy) affects only ticks damage, while buffs that are on character (for example Enrage) can affect both base and tick damage.
3. Sometimes last tick of DeepWounds is carried on to next DW even if it did it's damage. When this happens remaining damage is added to final tick value without doubling buffs like Trauma or Blood Frenzy but if it wasn't affected by Enrage it is now added.
4. Execute crits proc minimal (close to 0) DeepWounds on live. EDIT: as stated in this comment Execute crits generate normal DW, so behaviour from case 6 is currently without explanation.
5. If two crits happen at around same time, one of them can be "overlooked" in DeepWounds generation.