Peformed tests on my end:
- Testing with a captureActor set to a valid actor in the database: valid, no bug detected.
- Removing the captureActor note tag: valid, no bug detected.
- Setting the captureActor id to a value equal to or less than zero (0): invalid, bug shows up as in your screenshots, please see monster capture setup in this instance.
- Setting the captureActor id to a value greater than the number of actors in the database: invalid, bug shows up as in your screenshots, please see monster capture setup in this instance.
Only conditions 3 and 4 were able to replicate the bug on my end and this was due to setting a capture Actor id outside of what is defined in the RPG Maker database. I will be implementing an error throw for this but are those conditions valid on your end?
If you are not comfortable discussing this here, please private message me.