Describe the bug:

As part of the ops KPI review we've been investigating the following errors in ecs logs:

decode error: data read error: v2.errorRoot.Error: v2.errorEvent.Exception: v2.errorException.Stacktrace: []v2.stacktraceFrame: v2.stacktraceFrame.Vars: Read: unexpected value type: 0, error found in #10 byte of ...|length": [NaN, NaN, |..., bigger context ...| redacted ...", "common_length": [NaN, NaN, NaN, NaN, NaN, NaN, 27.0, 76.0, 76.0, 76|...

vars is defined as a flat mapping of local variables but NaN is not a valid type.

To Reproduce

I don't have steps to reproduce, this is part of the ops KPI review and was observed in the ecs logs.

Environment (please complete the following information)

The error has been observed in the following agent versions:

• apm-agent-python/6.18.0
• apm-agent-python/6.15.1
• apm-agent-python/6.13.2
• apm-agent-python/6.12.0
• apm-agent-python/6.10.0
• apm-agent-python/6.7.2
• elasticapm-python/5.10.1
• elasticapm-python/5.10.0

This happens on multiple apm-server versions.

Additional context

none