Not able to BlinkUp imps

I have a 7 imp002 which is mounted on PCB (have produced 100 of them - the others are sending data from concept test at customers). Now I’m trying to blink these 7 newly coated imp002’s. When I turn them on they’re just blinking “unsuccessful linkup”-code red blinking. Can’t contact them with the blinkup app - neither “clear config” or “new credentials” functionality. Something I’m not aware off? My last blinkup for devices was 1 month ago - maybe something new happend?

Thanks!

A solid red or rapidly flashing red LED indicates a power supply issue (see ‘Tips’, below)

From: BlinkUp Troubleshooting Guide (right under the BlinkUp codes).

The LED stays red or flashes red very rapidly? This is almost always a power supply issue. The device boots, turns the red LED on and then tries to activate WiFi. However, the WiFi power draw reduces the on-board imp’s operating voltage below tolerance and the imp resets. This continues ad infinitem. Check the power supply feeding your device.
From: BlinkUp Troubleshooting Guide (all the way at the bottom).

Do you have a way of making sure that the imp is getting the right supply?

Maybe you have a batch of ‘bad’ or marginal capacitors that you put on the boards. Like @reshef mentioned, measure the 3.3VDC voltage during the whole blinkup process.

A very common problem is that the fab stuffs the phototransistors the wrong way round, which makes them work very badly. Definitely worth checking!