Using Lubuntu 18.04 Bionic 32 bits.
The GPU is using vesa driver and USB keyboard.
Holding an keyboard key in few seconds is “automatically” unholded.
Using CPU power profile powersaver the issue happen in few seconds and selecting ondemand or performance are long time to unhold keys.
Only happen when using emulators. Not problems with text editors.
Another detail cpu resource is 25 % when using emulator.
On some machines there is an option to disable “stuck keys” in the BIOS. Maybe that is what is going on.? It doesn’t seem like a Lubuntu issue more of a hardware issue.
Can you please provide application names? This is a bit to large of a category to narrow down potential issues.
Linux is great but it can’t fix your hardware. If something is CPU intensive it will use CPU. Since you are on a 32bit machine I am guessing that the machine is low on resources for modern software demands. 25% doesn’t sound all that bad really depending on workload.
BIOS not has Stuck keys options.
The applications are console emulators (FCEUX, Gens, Stella and Zsnes).
Gens and Zsnes use extremely few CPU resources being less 40 %.
Not tested video players if also has the same issue.