Importing Old FBX files exported with FBX 6.1 (before FBX SDK 2011) and containing multiple animations will grow the memory usage exponentially with the number of animation takes in the file.

This is a bug in the latest FBX SDK (2020.3.1) and will be fixed in the upcoming update. This is out of our control (external to Unity) but is expected early March.

Temporary Workaround: Using the FBX Converter (https://www.autodesk.com/developer-network/platform-technologies/fbx-converter-archives) on the affected files to convert them from 6.x to 7.3 will avoid the issue

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# Open attached project with 2023.1.0a26
# While opening project, press "Ignore" and ignore errors
# See that memory usage by Unity is increasing

Result - Notice that editor gets stuck on importing "Idl3.fbx" or other fbx file. Memory usage keeps on growing, until mac asks to shut down some programs. In logs it doesn't show anything more except importing this model

Reproducible with - 2023.1.0a25 eac607654885, 2023.1.0a26 c80c0f25543e

Not reproducible with - 2023.1.0a24 f576cc309ca2

Reproduced on MacOS 12.2 and 13.1, Windows 10. (Happens on all OS but M1 is more affected)