What can be done?

1. Undervoltaged? Use the correct power supply

The issue might simply be the use of a power supply that is not powerful enough. This is often the case when using a power supply that is not an official Raspberry Pi power supply. If you see a little yellow lightning icon in SimplyPrint, OctoPrint or the warning "Undervoltage detected", switching to another / an official power supply is most likely the fix for you.

2. Allow your Pi to breathe

If your Raspberry Pi is encased or hidden away in a shelf, behind or under your 3D printer, or in general somewhere hot; let it breathe! The Pi needs to be able to get rid of its heat, so placing it somewhere with airflow, and not putting it in a closed off box or case with no holes goes a long way. It is, however, important to protect your Raspberry Pi from other electric components and static electricity, so using a case like the SimplyPrint Raspberry Pi case (Thingiverse link), where the Pi is protected, but still has holes for air is recommended.

3. Use a fan

Sometimes a Pi needs a bit of external help to cool down. Using a small fan that can be mounted directly onto the Pi, and be powered by it, is a good idea to keep your Pi cool and extend its lifespan. There are multiple different fans to choose from, but just pick whatever fits your setup and your Raspberry Pi model best; find a fan that fits here.

4. Use heat sinks

A "heat sink" is a little piece of metal that helps transfer heat away from the Raspberry Pi. A small heat sink is either applied directly on top of the different core components of the Raspberry Pi, or you can go with a large heat sink that covers multiple components or even the whole Pi. You can also combine fans and heat sink(s) for the optimal Pi-cooler. Find a heat sink for your Pi here.

5. Limit what's running on the Pi

If you have done all you can to ensure the "outside" health of the Raspberry Pi is good, the next step is to look on the inside; if the "CPU" usage or "memory" is running high, your Pi might be chewing off more it can bite. Try and limit what the Pi is doing, so if you have a camera attached to your Raspberry Pi, try and unplug it to see if that helps - a webcam can be a lot for older Pi models to run. If you're running multiple printers from a single Pi, maybe get a Pi per printer, or run fewer instances on the Pi with problems. Furthermore, if you're using the Pi for other purposes as well as 3D printing (running Smart Home / IOT or other services / servers), it just might be too much for your Pi to handle - try and cut off whatever is not necessary.

6. Try a fresh install, or a new SD card

Sometimes a fresh installation of the Raspberry Pi software/OS can do a lot - and it's a good idea to try and swap out the SD card in the process as well, as a slow, damaged or just old SD card can have a big impact.

Conclusion

That was our list of things you can try to get your Pi in a better state! If you've had no luck with these potential fixes, seeing if a new and fresh Raspberry Pi performs better might be a good idea, to rule out that your Raspberry Pi itself is damaged.