question

Do you use one of these MC4 parallel cables with 4 inputs and 1 output?

I assume the panels have apprx. 30Vmpp, so for 1kW you have parallel currents of about 33A. This will be too much for the MC4 as you also suppose. So does the MC4 connector get hot, I mean really hot? If yes, then you have the problem, but if this is not the case, then the problem might be elsewhere.

If you are fine to put the connections into some box, then you could use almost all high current rated connections. A simple solution would be a screwterminal for din rail mount like Pollmann Main Line TerminalI. You can install this in a standard IP4x din rail enclosure. But keep in mind, that for those screwterminals you need ferrules.

But first you should check if this is really the problem before you spend money. ;-)

Re the 'theoretical peak output' of your panels, according to 'Energypedia' the Standard Test Conditions used by manufacturers to rate their panels are 25C cell temp, 1kW/m2 solar irradiance and Air Mass of 1.5 (i.e. solar noon in the spring and autumn equinoxes in the continental United States).
https://wiki.openmod-initiative.org/wiki/Standard_test_conditions

For comparison, I'm currently seeing 1744W Pmax (in remote Console) for a 1770Wp 45deg, due South, free-standing array at 53 deg N in the UK.

So, unless your in the polar region, 500W max for a 1060Wp array seems to say something isn't right? But, if you're around 500W down on what you might expect, then that's probably way too much to be lost in MC4 connectors alone.

I haven't bothered with MC4 given specialist tools needed and have instead used e.g. Wago 41A lever connectors in IP65 boxes.

Thanks Jetlag and Johnone for great input. Yes the panels generate 30V MPP so good to know that it's probably not the 4 MC4 input -->1MC4 output connectors causing the problem. they are incidentally not at all hot with panels in full noonday sun. I'm using an Epever 8420AN tracer MPPT and think that this may be the constraint as the manual says max 2 60 cell panels. I didn't know this when I bought the MPPT controller thinking that as long as I respected the max Voltage and Amps onputs specs I'd be ok. I guess I could buy another but would need to parallel the MPPT units up. Further thoughts welcome but thanks gain for already enlightening me on connection alternatives.

@conceptura You can just solder them together and cover with heatshrink. It’s not like you will ever routinely disconnect your panels. Just hard wire them and be done with it.