Well, back again!

It's just happened again. Three invoices created with sequential invoice numbers and transaction IDs, all with a minute of each other. This is on a PC that has just had all the temporary files/cookies/etc., cleared out as per QBO instructions.

What we noticed this time is the following error occurring, within a red error message box at the top of the invoice when trying to save it:

Something's not quite right

Cannot read property '_cachingStore' of null

QBO said they needed to see a full screen capture rather than the one I've attached, but I don't know what extra information they could take from that.

Look forward to hearing back from anyone!