<<<The drain pump was replaced 3 weeks earlier>>>
What other critical details have you left out or forgotten ?
Was the drain hose attached to a standpipe---and wrapped with tape to prevent water from gushing out?
A partially-restricted drain can give the symptoms you've described initially.
The main point here is that---we don't want other servicers and DIYers---to say:
"Hey my LG washer drains erratic too---let's check that little black hose-thingy at the top of tub."
The function of the anti-drainback hose is to prevent siphoning of water during wash---if the drain hose has been improperly installed (not inhibit draining---even if it becomes plugged).
I have never encountered a problem with a blocked anti-siphon tube *preventing drain*.
The original LG washers (which did not have a siphon tube) drained just as fast and reliably.
In 14 LG training seminars---not once has this been discussed as a possible "Slow or No Drain" issue.
An incorrectly installed drain hose---is a possibility to consider when servicing an LG washer with the complaint that you've described.