Yesterday, when researching accumulators the name shown in the research progress window was Unknown key:"technology-name.electric-energy-accumulators" 1 (see attachment). I didn't see this for other researches, but of course I didn't research everything.

[ Factorio 0.14.13 - OSX ]

Confirmed. It's now working.

But the level has a mistake: It is not possible to build Filter inserters, needed for Science pack 3. Only Stack filter inserters are available.

I can confirm it. When starting a new campaign I immediately get the error. I only unlocked TightSpot-5 on easy level (in v0.13).

[Factorio 0.14.8, OSX]

You beat my edit, clarifying just that... So it also doesn't work when starting "fresh".

It should be fixed in 0.13.18. The release notes say so. But still I get the same assertion error. Maybe because I'm playing the level on easy?

I get the error when I try to continue my save game from finishing lvl 4, but also when I start it fresh from Play>Start Campaign.

Yesterday I finished lvl 4 (v. 0.13.15) and could not continue to lvl 5 for the same reason. Also with v0.13.16 this is still the case. So it appears the fix didn't take.

Here's a savegame and screenshot https://we.tl/3O0KgMAE1E

[Operating system: Mac OS X 10.11.6]