Error concatenating strings in Field Calculator

[SFM_TravisBott]

Having a problem that should be simple but can't quite figure out what is going on. 

I am trying to concatenate three text fields into a fourth text field (Field1, Field2, Field3, landingField). One of the fields (Field3) is quite long and somehow is not willing to be concatenated with anything else. It can be calculated over (e.g. landingField = !Field3!) just fine, but it doesn't want to cooperate with anything else. 

For instance !Field1' + ' filler text ' + !Field3! does nothing. It doesn't throw an error...just nothing happens. However, !Field1! + ' filler text ' + !Field2! + ' more filler text.' works just fine.

I suspected the length of the field was the issue (Field3 is  2000 characters) but I upped landingField to 10,000 characters and same issue. And trying to adjust Field3 by using the .str() method or something similar doesn't seem to work. 

Any hints as to what gives?

[jcarlson]

I would check out the values in the given field. Are there nulls that could be throwing it off?

Have you tried a similar expression in Arcade?

[SFM_TravisBott]

I have not tried it in Arcade, but will do so. 

There are no null values - the fields are enforced in the survey they're submitted through. And each field can be calculated independently. It's really just the one long text field that doesn't want to be concatenated with anything else.