Studio stuck while debugging PickAction/PickBranch with SlowStep + ExecutionTrail


while trying to debug a different nasty problem I encountered situation, where debugger just stops executing.

I isolated the problem to this:
If you run debug file while having both Slow Step and Execution Trail ON, studio stops the execution process (like on timeouts or breakpoints) when encountering the Pick Activity.

Any other debugging combination works fine (SlowStep, ExecTrail, HighlightElems, LogActivities, ContinueOnErr), just these two options can never be turned on simultaneously, otherwise execution gets forever stuck on the Pick Activity.

Yes I know logMessageActivity is not ideal trigger nor activity. It has been simplified for demonstration purposes.

I am not sure whether this is studio problem or activity problem so feel free to swap the tags, but my guess it’s in the backend of .NET pick+pickbranch implementation since it acts weird in some other (very difficult to describe) situation:

different bug I encountered that might be related to wrong pickActivity implementation

My pickbranch randomly (sometimes every other execution, sometimes every 700th execution) throws uncatchable exception 0xc0000409 or 0xc0000005.

Involved activities I traced the error to: pickActivity and pickBranch and ElementExist.

It took me 3 days of hitting “debug” to replicate/encounter the error the last time so it is extremely hard to prove/demonstrate.

Tested on different computers: win10 (3 different PCs), winServer2016 (Azure); both from Orchestrator (robot) and from Studio (run and debug).


Vit Hlavacek

version: Studio Pro 2020.10.2 Community (non-PRO studio doesn’t have ExecTrail option)
run on: win10pro 64bit

Bonus question: If there is some kind of bug bounty program to incentify well documented bug reports?

Hi @vit.hlavacek,
Are you able to provide example project which could help us to reproduce this issue?

We don’t have such program at the moment. But if you wish to help us and share your knowledge and gain more RPA experience at the same time + a lot of more benefits you should consider to become our MVP :slight_smile:
More details here: MVP Program | UiPath

I thought screenshot “simplified for demonstration purposes” I provided was enough but alright,
here further simplified workflow file: debug.xaml (5.1 KB)

Please refer also to the


I cannot provide workflow for that bug at this moment though, but it looks like this:

openBrowser( seq( pick( pickBranch1( ElementExists); pickBranch2( ElementExists) ))) .

Posting the workflow wouldn’t probably make a difference since reproducing the issue is extremely random. (More in details in the first post.)