The EpEver line of MPPT solar charge controllers is an excellent value-for-money for some use cases. They cost about half as much as prettier, more-prestigious controlllers.

• the controllers can take massive overpaneling; the smaller units (≤40A) have documentation that allows +50% overpaneling¹⁾. The larger units show +200%²⁾
• the passive heatsinks are huge for their rated capacity
• accessories like display, temp probes, etc, are extremely inexpensive
• the current user manuals³⁾ are quite good

As with vans, all controllers have issues. This page aims to list known⁴⁾ issues with EpEver controllers.

They may not be a fit for all use cases, though. Consider these drawbacks in the light of your own intended scenario:

• the MPPT algorithm is not particularly robust
  • it will adjust to changing conditions, but it can be slow. One might say “plodding”.
  • it can be slow to react after long periods of no load - see this reddit post where I describe the phenomenon
  • it can get confused in complex solar conditions, as with partly-cloudy skies and high winds, or in breezes that move partial shade around on the panels. In these conditions Vpanel can fall to just above Vbatt, severely hobbling solar harvest.⁵⁾
• the large AN controllers (≥50A) have undersized terminal screws which can snap under overzealous tightening. IMO EpEver should update the design with hefty BN-series terminal screws.
• firmware does not appear to be field-upgradable without hacking
• Absorption duration cannot be zeroed out; the minimum duration is 10 minutes.

My epever often pulls pv voltages down to battery voltage acting like PWM. Getting really annoying now. It works okay with 12v and 17.5v panels, but the bigger panels with a voltage of 35v present a problem on cloudy days. It drags thr voltage down, and doesnt let it back up until i reset the unit. It then lets the panels back up to proper voltage and starts producing decent power again. (source)

I have the 4215bn with mt50, and whenever I connect my solar panels in series (2x100w), it will display the accumulated voltage for a few seconds (40w) under the pv icon, then it will go down to between 13-20v, immediately, even if the weather hasn't changed (no clouds and fulll sunlight). (source)

I'm sending my tracer3215bm back today as the mppt tracking issue is a blocker for me. I have 3 60 cell panels in series for a total of around 90v pv. This is on a 24v system. One morning it will work fine and the next it will get stuck down around 28v and never increase leaving my output at a fraction of what it could be. The only way to get it to increase the pv voltage is to disconnect the pv array momentarily. (source)

Facing the same with Epever (12v system) in bad conditions it will pull the 2x 18v panels in series down to single panel voltage range of 14-18v. I resorted to taking my panels in parallel (which sucks due to higher current and cable losses), which wastes less. In northern europe this is a killer for my batteries in winter, as i cannot even maintain a proper float voltage with my equipment attached. (source)

The system seems to work as it should most of the time. On occasion in full sun the charge controller shows a lower voltage ie 26.4 v about half of what it typically does in full sun. If I unplug everything and plug the panels back in it will return to the higher voltage around 60v and begin working normally again. (source)

I used a epever 3210an controller for about a year. I was using lead acid. With the same issues you're having. A passing cloud will cause the charge controller to get lost tracking. And the array voltage will drop and get stuck. Having to constantly watch then unplug and reconnect to get it going again. (source)