I had exactly the same problem with the March update and Linux Mint. GUI reset did not work, so I checked out the XML and also found width = -1 or to be more precise:
<entry>
<string>name.abuchen.portfolio.ui.views.StatementOfAssetsViewer</string>
<config-set>
<configurations>
<config>
<uuid>797b53e5-2129-404c-95cb-8e994426f094</uuid>
<name>Standard</name>
<data>{"items":[{"id":"0","width":92},{"id":"1","width":218},{"id":"12","width":80},{"id":"attribute$031f82b2-61f2-4b29-803e-2fe3e1ea3a32","label":"PEe 26","width":56},{"id":"attribute$6c6f04cc-4397-4e0f-b6e0-d0631ec7d9da","width":56},{"id":"attribute$ab005510-9a64-491b-adee-afea7ed7f9c5","label":"V/G/D","width":-1},{"id":"attribute$3e7cb3d8-e19d-45be-a4cc-76dfe3cac216-daysbetween","label":"Kz.-Alter","width":63},{"id":"4","width":97},{"id":"ttwror","label":"%1 Tag","option":"T1","sortDirection":1024,"width":84},{"id":"ttwror","label":"%1 W","option":"T5","width":80},{"id":"9","width":109},{"id":"5","width":101},{"id":"note","width":130},{"id":"6","width":80},{"id":"7","width":109}]}</data>
</config>
</configurations>
</config-set>
</entry>
I replaced the value by 1, saved the XML and then could open it without any problems.
Hope this helps finding the actual issue.
PS:
Version: 0.82.1 (März 2026)
Platform: linux, x86_64
Java: 21.0.10, Flathub