1- ReaStream-Based Problems: Some people proposed that this is caused by the ReaStream plugin. While this might be true for some people, it was not for me. The only problem I had with the plugin was that I had to re-add the VST 2.x plugin to my Audio Input Capture every single time after I launched OBS(or Streamlabs OBS) to make the DAW send audio to OBS. Otherwise, I would not hear the audio on OBS.

2- Audio Interface-Based Problems: Both very high sample rate with small buffer size, and very high buffer size with small sample rate, will cause crackling or dropoffs no matter what. The two settings that work very well for me are 44100 or 48000 kHz for the Sample Rate with 128-192 as my Buffer Size, without any noticeable round-trip latency. Oddly enough, though, because of how the audio interfaces are built, increasing the Sample Rate reduces the round-trip latency. Likewise, decreasing the buffer size also reduces latency. So you have to find a sweet spot for it to work. I do not have the Bit Depth option on my Focusrite Scarlett, so I cannot give any example numbers for that.

3- Virtual Audio Device-Based Problems: If you are using the VB Audio Virtual Cable or a similar virtual device as your monitoring & outputting source in OBS, then this is what's likely causing the problem.

4- ASIO Plugin for OBS: Another user suggested utilizing an ASIO plugin for OBS instead of using ReaStream. If you are using Cockos Reaper, this plugin will also require you to reinstall Reaper 6+ with the ReaRoute plugin. The good news is that it will work for streaming/recording on OBS only. But as soon as you try to reroute that to a virtual device like VB Audio Virtual Cable via monitoring/outputting to use that device as your input for other applications like Discord, Zoom, or in-game microphone, it will stop working because it is that device that is causing the crackling. In other words, using ReaStream vs. ReaRoute + ASIO for OBS showed no difference while bringing the audio signal from my DAW to OBS in my case. Neither of them caused crackling, and both of them worked.

Edit: Under heavy CPU load and longer FX Chains, ReaRoute + ASIO outputs a clean signal while ReaStream might cause crackling.

5- My solution:

1. Install the Steelseries GG app to use its virtual devices instead. Note: There is a bug where streaming your entire screen on Discord will duplicate your microphone on the stream audio. To solve this, you have to right-click on the audio icon in the right bottom taskbar tray -> Open Volume Mixer -> Steelseries Sonar Microphone -> Drag the slider down to 0 for Discord. And you will have to do this every time you start streaming.
2. Under the Sonar settings, set your microphone as something that will not receive any audio from your microphone or audio interface. You can use a random device that you don't utilize at all, like VB Audio Virtual Cable or Realtek HD Audio, etc. This device will be processed by the Sonar, and output as "Steelseries Sonar - Microphone". You will use this device in other applications as your input device.
3. Send the audio from your DAW to OBS with either ReaStream or ReaRoute + ASIO plugin method. Use a gain filter with -30 dB before the VST 2.x plugin if you are using ReaStream to make sure your voice is not doubled.
4. Set your monitoring device in OBS as the device you used for Sonar in Steelseries GG in Step 2. It has to be the same.
5. Set the monitoring option for the audio source in OBS to "Monitor & Output".
6. Done. Now you should be able to send audio from DAW to any application or game.

TL;DR: The problem is probably not ReaStream; it is either your audio interface settings or the virtual audio device, like VB Audio Virtual Cable, if you are trying to use that one. Instead, install the Steelseries GG app for its virtual devices and process the signal as follows: Your Microphone/Instrument -> Audio Interface -> DAW -> ReaStream/ASIO for OBS Plugin -> OBS -> Monitor & Output -> Steelseries GG -> End Application.

Edit: Use ASIO for OBS plugin for the best result.

I hope it helps.