Panels in series go to 0v?

I'm hoping I'm just doing dumb here. My neighbor and I have the first set of 4x240 watt panels wired 2s2p, and working fine. This is a known set of hardware that we are only moving from my house (I upgraded massively) to his house. Same hardware same setup. When I checked the output on each panel prior to wiring it in series first, all are producing 32.1-32.4v. However, when I wire them 2s, both sets go to 0v on the meter (Klein cl310). When I separate them back to single panels it's still at 0v, but if I check again (next day) I get 32v again? I tried series again this morning and same thing happened. WTH?

Are the panels in full sun with no shade at all like your shadow when you are checking them?

Measurement error, wiring error, or MC4 connector insertion problem.

It is basically out of the question that the panels are actually going to 0v in sun.

Checked at full sun. I only get 0v when in series, 32v when checked individually. I'll verify again that the MC4 connectors are clean and connected well.

Newenough said:

Checked at full sun. I only get 0v when in series, 32v when checked individually. I'll verify again that the MC4 connectors are clean and connected well.

Click to expand...

MC4 terminal can slide back inside the connector and not make contact. Unbelievable design flub by the Swiss.

Thanks. I'll put new connectors on. These are probably 10yo panels at this point, and probably pretty baked. Unplugging them may have loosened them as well. Good idea.

Thanks for the suggestions. Replaced all the connectors. Reading correctly now.