I'm certainly no fcpxml expert but are you sure you can use floats for duration? The docs for XML 1.10 say either a rational number or a whole number. Maybe it's changed for 1.11, but I can't find those docs.
From Document Type Definition | Apple Developer Documentation
<!-- FCP XML Interchange Format, Version 1.10 -->
<!-- Copyright (c) 2011-2021 Apple Inc. All rights reserved. -->
<!-- COMMON ENTITIES -->
<!-- 'time' attributes are expressed as a rational number of seconds (e.g., "1001/30000s") -->
<!-- with a 64-bit numerator and 32-bit denominator. -->
<!-- Integer 'time' values, such as 5 seconds, may be expressed as whole numbers (e.g., '5s'). -->
<!ENTITY % time "CDATA">
Your fcpxml has a decimal time:
<asset id="video0" format="r1" name="10 x(25).mov" ... duration="121.74s">
Importing your fcpxml into FCP 10.7.1 and then re-exporting it, the duration for this asset is converted to:
<asset id="r2" name="10 x(25).mov" ... duration="73044/600s"
which is 121.74. But since your fcpxml does actually import maybe this is not the problem.
Importing this re-exported fcpxml comes in with no complaints about edit boundaries but 4 new complaints about edits.
Info.fcpxml Invalid edit with no respective media. (/fcpxml[1]/library[1]/event[1]/project[1]/sequence[1]/spine[1]/asset-clip[20])
Info.fcpxml Invalid edit with no respective media. (/fcpxml[1]/library[1]/event[1]/project[1]/sequence[1]/spine[1]/video[3])
Info.fcpxml Invalid edit with no respective media. (/fcpxml[1]/library[1]/event[1]/project[1]/sequence[1]/spine[1]/asset-clip[23])
Info.fcpxml Invalid edit with no respective media. (/fcpxml[1]/library[1]/event[1]/project[1]/sequence[1]/spine[1]/asset-clip[24])
The ends of both the original fcpxml and re-exported-then-imported fcpxml timelines look odd and to me could be duration or offset calculation problems. If it were me, I'd start with simple, whole second durations to make sure duration and/or offset calculations are correct.
Original fcpxml
Re-exported fcpxml