Possible something dripped on those leaves? like water with fertilizer mixed in?
as long as you aren't watering too frequently or incompletely, can rule that out. you know your habits. if you aren't fully saturating pot and waiting for an approriate dryback that can cause weird leaf symptoms typicaly along/around the veins.
doesn't look like a pathogen, but if worried, snip it off and carry on.
if it's new to the sun, that could be light damage, too. an indoor plant can't handle full sun without adapting to it slowly.