First time making plum wine, followed a recipe and instructions and one day one have come to find sediment and light brown liquid in my airlock. Should I be worried?
Nothing to worry about unless it overflows.
When fermentation is strong, small particles can get pushed out with the co2. It does not look nice but is harmless.
If the airlock overflows it will make a mess. This can easily happen if fermentation is very strong and there is not enough head space in the fermenter. In that case you should use a blowoff tube, i.e., instead of the airlock put a tube in and lead that to a bucket with some water so that the end of the tube is submerged. If you cannot build a blowoff tube, put the fermenter in a tub or such to contain the mess.