Unity Issue Tracker - "Unrecognized block header in profiler data file, stopping deserialization" error is shown and no more profiler data is recorded when the Player is connected and profiler recording is enabled/disabled few times

Active

Under Consideration for 6000.5.X

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Found in

Issue ID

Regression

"Unrecognized block header in profiler data file, stopping deserialization" error is shown and no more profiler data is recorded when the Player is connected and profiler recording is enabled/disabled few times

-

Jan 15, 2026

Steps to reproduce:

Create a new Unity project using the Universal 3D template
Go to File > Build Profiles
Enable "Development Build" and "Autoconnect Profiler"
Build and Run the project
Once built, observe the data is being recorded in the Profiler
In the Profiler, click on the recording button 4 times (to disable - enable - disable - enable)
Focus back on the Player and observe the Console and Profiler

Actual results: "Unrecognized block header in profiler data file, stopping deserialization" error is shown and no more profiler data is recorded

Expected results: No error and the profiler data continues recording

Reproducible with versions: 2023.1.0b1, 6000.0.66f1, 6000.3.5f1, 6000.4.0b4, 6000.5.0a5

Tested on (OS): Windows 11

Notes:

Could not reproduce on macOS 26.2
It appears to be caused by the fact that no data is gathered after the first re-enablement