I second this. Was playing an 1890 Germany Campaign and after I wiped out both UK and France, I kept hitting next turn to see how fast research and GDP growth is. After an initial rather fast-ish surge to 9.363 Billion, my GDP actually started shrinking despite still having economic growth of +14%.
I kept going for a bit to see how it would develop, and even in like the mid to late 1920's my GDP was still slowly declining, despite positive economic growth, to 9.34 billion. At this point my transport capacity was at 200%, so that slider was at the default middle position, my crew training was also in the middle, and research maxed out.
I had scrapped my entire fleet, and was still at a negative monthly balance. I also took some decisions that were supposed to increase naval budget %, but they didn't do anything. Neither did GDP % increase decisions.
This is especially a problem, since the hard-cap doesn't go away. If you start a campaign with Germany in 1920, the starting GDP is I believe 30 Billion, but just like with the shipyard construction amount which doesn't go up as the years progress, the GDP cap also doesn't seem to increase, which means that no nation will be able to actually afford the newer ships if the campaign is started in 1890, since the GDP caps don't increase and thus the monthly budget is far too low.