I've been playing KSP for 1,300 hrs and have used MechJeb for most of that time. Thank you for your MechJeb work, it is indispensable. I keep KSP and mods up-to-date by checking Curseforge daily. I'm currently running a fairly new PC Career game. haven't had any problems until KSP 1.10.1 and MechJeb2-2.11.0.0. MechJeb2 now behaves erratically. Many times it will generate a maneuver, I click Activate, and the maneuver disappears. As a work-around I'll have it generate the maneuver and then I'll do it manually. This can happen even with the Advanced Unmanned Tech research unlocked and flying the RC-001S RGU, so I know it has the capability to do the maneuver, unlike a low-level pilot. The biggest problem is the Rendezvous Autopilot causing the MechJeb2 windows to freak out by radically blinking. I have to close out of it.

I've never seen MechJeb act so unreliably. I have bizarre fuel transfer issues too, but I doubt those are unrelated to MechJeb2. Here are the mods I'm running, pretty standard stuff: KAS_v1.7, KPBS-1.6.12, KerbalAlarmClock_3.13.0.0, KIS_v1.26, SCANsat-v20.4, SurfaceLights_v1.16. I've uninstalled and reinstalled the game, and verified files.

"Help me Obi wan Kenobi, you're my only hope."

all the code that was throwing/logging in this bug no longer exists.

I've noticed the autopilot messing up too for MechJeb 2.9.2 (the rendezvous planner and maneuver planner are fine)

(all tests were made using tolerance = 0.1 m/s)
The Rendezvous Autopilot can't seem to properly assess what to do after matching planes, with this as the log spam:

[ERR 17:20:59.303] MechJeb module MechJebModuleRendezvousAutopilot threw an exception in Drive: System.TimeoutException: Brent's rootfinding method: maximum iterations exceeded
at MuMech.Brent.Solve (MuMech.BrentFun f, System.Double a, System.Double b, System.Double rtol, System.Double& x, System.Double& y, System.Object o, System.Int32 maxiter, System.Int32 sign) [0x001e3] in <4cdbe337c6aa43d0bc3552436a95c969>:0
at MuMech.OrbitalManeuverCalculator.DeltaVAndTimeForHohmannTransfer (Orbit o, Orbit target, System.Double UT, System.Double& burnUT) [0x00102] in <4cdbe337c6aa43d0bc3552436a95c969>:0
at MuMech.MechJebModuleRendezvousAutopilot.Drive (FlightCtrlState s) [0x00650] in <4cdbe337c6aa43d0bc3552436a95c969>:0
at MuMech.MechJebCore.Drive (FlightCtrlState s) [0x00048] in <4cdbe337c6aa43d0bc3552436a95c969>:0

[ERR 17:20:59.326] MechJeb module MechJebModuleRendezvousAutopilot threw an exception in Drive: System.TimeoutException: Brent's rootfinding method: maximum iterations exceeded
at MuMech.Brent.Solve (MuMech.BrentFun f, System.Double a, System.Double b, System.Double rtol, System.Double& x, System.Double& y, System.Object o, System.Int32 maxiter, System.Int32 sign) [0x001e3] in <4cdbe337c6aa43d0bc3552436a95c969>:0
at MuMech.OrbitalManeuverCalculator.DeltaVAndTimeForHohmannTransfer (Orbit o, Orbit target, System.Double UT, System.Double& burnUT) [0x00102] in <4cdbe337c6aa43d0bc3552436a95c969>:0
at MuMech.MechJebModuleRendezvousAutopilot.Drive (FlightCtrlState s) [0x00650] in <4cdbe337c6aa43d0bc3552436a95c969>:0
at MuMech.MechJebCore.Drive (FlightCtrlState s) [0x00048] in <4cdbe337c6aa43d0bc3552436a95c969>:0

[ERR 17:20:59.349] MechJeb module MechJebModuleRendezvousAutopilot threw an exception in Drive: System.TimeoutException: Brent's rootfinding method: maximum iterations exceeded
at MuMech.Brent.Solve (MuMech.BrentFun f, System.Double a, System.Double b, System.Double rtol, System.Double& x, System.Double& y, System.Object o, System.Int32 maxiter, System.Int32 sign) [0x001e3] in <4cdbe337c6aa43d0bc3552436a95c969>:0
at MuMech.OrbitalManeuverCalculator.DeltaVAndTimeForHohmannTransfer (Orbit o, Orbit target, System.Double UT, System.Double& burnUT) [0x00102] in <4cdbe337c6aa43d0bc3552436a95c969>:0
at MuMech.MechJebModuleRendezvousAutopilot.Drive (FlightCtrlState s) [0x00650] in <4cdbe337c6aa43d0bc3552436a95c969>:0
at MuMech.MechJebCore.Drive (FlightCtrlState s) [0x00048] in <4cdbe337c6aa43d0bc3552436a95c969>:0

(repeats until the autopilot is turned off)

If the autopilot is turned on after a Hohmann transfer, I usually expect match velocities at closest approach from it. But if it wants to fine tune the closest approach, it violently runs the engines and the following log spam appears:

[LOG 17:03:02.293] [MechJeb] DeltaVAndTimeForBiImpulsiveAnnealed Check1: minDT = 0 maxDT = 7073.52703960536 maxTT = 1233.50848325288 maxDTplusT = Infinity
[LOG 17:03:02.293] [MechJeb] DeltaVAndTimeForBiImpulsiveAnnealed target.patchEndTransition = FINAL
[LOG 17:03:02.293] [MechJeb] DeltaVAndTimeForBiImpulsiveAnnealed o.patchEndTransition = FINAL
[LOG 17:03:02.293] [MechJeb] DeltaVAndTimeForBiImpulsiveAnnealed Check2: minDT = 0 maxDT = 7073.52703960536 maxTT = 1233.50848325288 maxDTplusT = Infinity
[LOG 17:03:02.326] iter = 20
[LOG 17:03:02.328] iter = 82
[LOG 17:03:02.328] iter = 1
[LOG 17:03:02.328] iter = 8
[LOG 17:03:02.328] iter = 2
[LOG 17:03:02.330] iter = 100
[LOG 17:03:02.330] iter = 1
[LOG 17:03:02.330] iter = 1
[LOG 17:03:02.332] iter = 100
[LOG 17:03:02.333] iter = 100
[LOG 17:03:02.333] iter = 3
[LOG 17:03:02.334] iter = 13
[LOG 17:03:02.335] iter = 100
[LOG 17:03:02.336] iter = 100
[LOG 17:03:02.337] iter = 1
[LOG 17:03:02.338] iter = 100
(continues for hundreds more lines)

update: no rendezvous issues on beta 2.11 so far