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Consequences of driving with manual locking hubs out of sync?

I drive a '92 Ranger 4wd. I locked both hubs in about 6 wks ago for winter (& double-checked while doing so). Have used 4wd a few times since; once had slight weird sound/feel while engaging, but since then no problem. Driving on dry clear road today–2wd–heard “tssh tssh tssh tssh THUMP” about 3 times in a row at 35mph; the thump could be felt in the cab, but I didn’t run over anything. Stopped, parked and checked under hood, under all sides/corners of chassis, found nothing amiss. About 1/4 mile further on heard a whirring noise at about 15mph at the right front but it went away at higher or lower speeds. Once back in my driveway, checked hubs and found left front engaged, right front “free”. If I’ve been driving on it that way for a couple of weeks around town, but rarely at freeway speeds, what is the potential for serious damage (and are my symptoms today related to the hubs being out of ‘sync’)? (I have no reason to think that someone may have maliciously unlocked the right hub, but I’m pretty careful when engaging and freeing the hubs, so I can’t see why they’d be in different states suddenly.)