Ran into two possibly related issues:

1. Have a contract where I need to run the Passive Exposure scan while landed at Kerbin. Launched a ship, attached the plate, and experiment. Started the experiment. Hit 100x and waited for ~10 days in game. Exposure stayed at 0.0

2. Recovered, and re-launched. Setup the plate, and experiment. Hit "Start Experiment" the plate unfolded but the "Start Experiment" button stayed, and the exposure bar never appeared.

Currently running v.0.8.1 through CKAN

I'm experiencing the same problem. Experiment starts and deploys, button resets back to "start experiment" immediately after deployment. Exposure stays at 0.0.

KSP1.7.3.2594, NEOS 0.8.1 installed via CKAN.

Installed mod list mods.ckan.zip

Save folder KSX.zip - the only vessel in orbit has PEC and experiments attached ready to debug.

Log file KSP.log

Looks like the problem is caused by the absence of kerbal alarm clock.

I've installed latest KAC (for KSP 1.6) and now my experiments work normally.
This can be counted as a workaround, although NEOS shouldn't fail without KAC installed :)

Sorry! For some reason I didn't get notified of this issue.

Thanks so much for the analysis and logs etc (nobody on the forum could be arsed). Now I can fix it.

Fixed; sorry it took so long, been so busy with real life.
The log showed the issue immediately so thanks for that.