I think it is partly this. If I uncheck this option the notifications for R&D don't go away (instead you get a sound alert and the message for R&D completion still appears at the bottom):
R&DUnchecked.png

Also that part where is says your Blazer is complete also still appears even when you ...

Some things you can try:

- Take over the city government and optimise the road network, you often don't need as many roads as you need, sometimes demolishing roads and moving around buildings can help you fit in additional structures.
- Zoning controls - you can try limiting the amount of zoning ...

Factory Capacity Modifier=500 in script maybe too, so you need less factories making same thing

I loaded your save game but couldn't trigger the error. If you encounter it again, please let me the steps you did for triggering it.