Updating from v3.9.10 to v4.0.0 broke percentage rollouts

[kupresk14]

Hello! Just wanted to get this noted. We have been using a percentage rollout for a while on v3.9.10 with success. We updated from v3.9.10 to v4.0.0 last week and it appears that it broke our percentage rollout. Users started receiving False for our feature flag only despite no rule or code related changes. We were previously doing 10% and 50% splits for a month without issue.

I tracked our flagged screen events coming through and the was essentially a 100% drop-off after we updated the package.

We are on the latest Flutter version 3.35.6

I went ahead and reverted back and everything started working as expected again.

Tested by uninstalling and re-installing our app on both Android and iOS repeatedly in a prod environment - our target is the device install_id and the difference in UI happens right away on app launch, so we could tell right away.

Also, it appears that v4.0.0 has no release notes within your Github, so maybe there's something different that just wasn't noted at all.

Thank you very much!!

[vazarkevych]

Hi @kupresk14. Please let us check that and we will write to you.

[kupresk14]

Hi @kupresk14. Please let us check that and we will write to yo

Any update on this?

[vazarkevych]

Hi @kupresk14 . Sorry for the delay, we will today status on this.

[vazarkevych]

Hi @kupresk14,

Thank you for reporting this issue.

While we weren't able to reproduce the exact scenario, we can confirm that the FNV-1a hash function implementation was incorrectly changed in a recent release, leading to hash mismatches with the JavaScript SDK.

We have provided an update to this method to precisely align it with the original JS implementation, ensuring 32-bit arithmetic and correct character processing.

You can find the fix here: PR

Could you please test this updated implementation and confirm if it resolves your issue?

We suspect the problem was caused by how the previous Dart implementation handled character codes (specifically 16-bit vs 8-bit processing), which is now corrected to match the standard behavior expected by your server/backend.

Thank you for your help!

[kupresk14]

I will test this out as soon as I can, thank you very much for the update!!

[vazarkevych]

Hi @kupresk14 . Could you please tell if you have a chance to recheck that?

[vazarkevych]

Hi @kupresk14 . Do you have a chance to check?

[kupresk14]

Apologies! Updated and looks like it should be all good now. Thank you very much for the help and update on your end!