Hello! This issue was noticed in svgo v1.0.5.
Option "collapseGroups" (or "Collapse useless groups" in SVGOMG) removing
Attached file demonstrates the problem -- just try to compress it with and without "collapseGroups" option.
I'm running into this same issue.
<defs>
<filter id="a">
<feDropShadow dx="0" dy="25" stdDeviation="25" flood-opacity="0.65" />
</filter>
</defs>
is being turned into this:
<defs><filter id='a'/></defs>
Most helpful comment
I'm running into this same issue.
is being turned into this: