Change in participant grouping backend causing new error?

[CarsonGMR]

Hi,

After a summer hiatus, I checked on an experiment last week hoping to start it back up again -- when I ran it in preview mode, it seemed to work just fine. Having made no changes, this week, the preview directs me to a page saying "Sorry, but we encountered an unexpected error upon processing your request." No syntax errors or anything else pop up.

Through process of elimination, it seems like the study preview works fine if I take out the participant grouping option. Was there some kind of recent change to participant grouping that might have caused this change? Or anyone else having a similar issue?

As always, thanks for the great work FF team + community!
Carson

---

For example that demonstrates the issue, the original procedure looked something like this:

Code:

  "block_sequence": [
    "InstructionBlock",
    {"DomFirstSwitch":
    {"dex": ["TestingBlockR", "TestingBlockL2"],
      "sin": ["TestingBlockL", "TestingBlockR2"]},
    "DomFirstCont":
    {"dex": ["TestingBlockR", "TestingBlockR2"],
      "sin": ["TestingBlockL", "TestingBlockL2"]}
    }
  ]
 

In the above snippet, the InstructionBlock includes a question asking for handedness (dex/sin), while DomFirstCont and DomFirstSwitch are two participant groups. Code including the participant groups is directed to the error screen (after I select either DomFirstSwitch or DomFirstCont in the preview prompt to choose a group).

Code:

  "block_sequence": [
    "InstructionBlock",
    {"dex": ["TestingBlockR", "TestingBlockL2"],
      "sin": ["TestingBlockL", "TestingBlockR2"]}
  ]

After removing the participant groups, like in the above block sequence, the preview works again.

[Ting]

Thanks for the report! We'll look into this right away and fix it. It seems to be only affecting preview but not live sessions, which is kinda ironic considering what "preview" is meant for.

[Ting]

Hello again - we've fixed the bug, and the servers will be updated overnight. It should work tomorrow after about 3am on the east coast. Thanks for letting us know about it!

[CarsonGMR]

Thanks for such swift response! Great news!