One contributing factor was likely the (IARU HF World Championship?) contest on this weekend. This usually boosts both activity and TX power and makes operators pull all-nighters.
But why I'm really here is that I want to emphasize on (antenna) takeoff angle:
20m normally closes in the late evening around sunset.
That's what I was thinking too for the first 40 years of SWLing.
Imagine my surprise when I found out the opposite, just of all in the past sunspot minimum!
The mechanism is pretty simple - the MUF also depends on "angle of incidence" - signals at NVIS angles have a lower MUF than signals bouncing off the ionosphere at a flat angle. Now when the MUF is decreasing during night (or isn't terribly high in first place, due to a lack of solar activity during a solar cycle minimum) two things happen: 1) most of your "radio neighbors" go to bed and 2) the ability of the ionosphere to reflect shorter distance signals from steep angles decreases (that's one reason why 80m is such a "night band" - the MUF rarely sinks that low). What's left are signals coming in at very flat elevation angles from the far points beyond the horizon. They are usually not that loud but they are there!
Now there are a few more factors playing a role in this, like your location (latitude!) on the planet but your antenna is the most important one: Basically, most contraptions us mere SWLs string up and put out for an antenna are not exactly great (sensitive) at low elevation angles. In fact, in most cases it's pretty hard to achieve ideal radiation (or in case of reception, sensitivity-) patterns for DX and in case of horizontal wire antennas, an antenna height of 1/2 lambda is needed to achieve at least
some low angle sensitivity. Another example are small magnetic loops (SMLs): They give you generally consistent vertical patterns much more independent from antenna height and ground conductivity but this is also their general disadvantage -- they never give you that much signal from low elevation angles even if you put them up high. The result is what I experienced most of my life - after sunset, the MUF goes down, signals coming in from steeper angles die off and what's left is a band looking empty....unless there's a really "big gun" transmitting on the other side.
Fast forward to 2017-18: I became a "DX nomad" and started experimenting with antennas at the coast. This is important because this location gives me low noise and a very conductive ground. What I didn't know back then was that putting up any horizontal wire antenna there is even worse - the better the ground, the steeper their vertical pattern becomes when they are not at their optimum height over ground. An SML was much better than that but the hobby still was a bit boring after sunset unless the conditions were somewhat "elevated". When I was too lazy to put up much of an antenna using the 30ft fiberglass pole I bought for getting some elevation for either dipoles or the SML one day, I just ran a vertical wire up that pole and that changed things dramatically!
It took me quite a while to understand that: The very conductive ground near the ocean freed me of the need for radials or a ground network to make this simple vertical monopole antenna work just the right way to make the nights surprisingly exiting, it has a quite flat, donut-shaped radiation pattern without these extra complications. Again, this was at the bottom end of cycle 24 and all of a sudden the nights were actually much more exiting than the days, quite often I heard
all continents in one night and - unless the sun had a little hickup - the generally quiet space weather made these basic "solar minimum" conditions very consistent! I started spending a lot of nights out there and even in case of a little geomagnetic disturbance, only 17m really "closed" a few times, 20m just suffered some degradation most times but almost never really shut down.
The reasons for that are: A flat vertical antenna radiation pattern more than anything else, and low QRM so the generally weaker, distant nighttime signals don't drown in it. The proximity to the ocean adds ~10dB of gain as a sweet icing on the cake, but that won't do much good without a flat vertical antenna pattern.
