Without any changes to the configuration or the LightBurn file, the problem is unlikely to have anything to do with those, so hardware is the immediate suspect.
If you’ve been using the laser for a couple of years, the tube is likely to be reaching the end of its lifetime and has begun operating erratically. Because it’s intermittent, this may be hard to verify, but the general process is to measure the beam shape at the first mirror.
A quick introduction:
A simpler problem could be focus lens working loose (or shattering!) inside the laser head. Take a look in there to make sure everything is OK.
While you’re poking around, check all the mirrors to verify they remain properly secured and aligned.
Also: are the pictures oriented the same way they’re engraved, with the scanning direction going left-right across the picture?