These investments would be considered by the French tax authorities to be similar to assurance vie (AV) policies.
There is a specific box on the tax declaration form in which to declare AVs held overseas, box 8TT (at the end of the main 2042 declaration if declaring on paper forms).
If declaring by paper, the tax offices have asked for a list of such AVs to be attached to the annual tax declaration if they were opened, closed or “modified” during the year. The online declaration should provide an appropriate space for the list.
In my view, as there is this specific box for AVs, the 3916, and corresponding box to tick 8UU, only relates to “accounts” and not investments. Note that all foreign accounts now have to be declared each year, “used” or not, and whether or not they generated interest. Certainly, the law only refers to a compte and not terms such as placement (investment) with regard to the 3916.
It is possible there is a translation issue, causing the tax office to consider the bond to be an account. Having said that, if the issue is that the tax office considers the existence of the bonds should have been notified, by whatever means, and you did not do it, then yes, it would be entitled to fine you €1,500 per undeclared ‘contract’.