Customer import fails with duplicate ID in WordPress

Plugin imported two customers and then failed on subsequent. Excerpt from error log.

[2025-09-25 15:39:02] [961914011712]Customer exists, WP User ID: 4
[2025-09-25 15:39:02] [1101518143552]Customer exists, WP User ID: 5
[2025-09-25 15:39:03] [961914011712]Customer exists, WP User ID: 4
[2025-09-25 15:39:03] [1101518143552]Customer exists, WP User ID: 5
[2025-09-25 15:39:04] [961914011712]Customer exists, WP User ID: 4
[2025-09-25 15:39:04] [1101518143552]Customer exists, WP User ID: 5
[2025-09-25 15:39:05] [961914011712]Customer exists, WP User ID: 4
[2025-09-25 15:39:05] [1101518143552]Customer exists, WP User ID: 5
[2025-09-25 15:39:06] [961914011712]Customer exists, WP User ID: 4
[2025-09-25 15:39:06] [1101518143552]Customer exists, WP User ID: 5
[2025-09-25 15:39:07] [961914011712]Customer exists, WP User ID: 4
[2025-09-25 15:39:07] [1101518143552]Customer exists, WP User ID: 5
[2025-09-25 15:39:08] [961914011712]Customer exists, WP User ID: 4
[2025-09-25 15:39:08] [1101518143552]Customer exists, WP User ID: 5
[2025-09-25 15:39:09] [961914011712]Customer exists, WP User ID: 4
[2025-09-25 15:39:09] [1101518143552]Customer exists, WP User ID: 5
[2025-09-25 15:39:10] [961914011712]Customer exists, WP User ID: 4
[2025-09-25 15:39:10] [1101518143552]Customer exists, WP User ID: 5
[2025-09-25 15:39:11] [961914011712]Customer exists, WP User ID: 4
[2025-09-25 15:39:11] [1101518143552]Customer exists, WP User ID: 5
[2025-09-25 15:39:11] [961914011712]Customer exists, WP User ID: 4
[2025-09-25 15:39:11] [1101518143552]Customer exists, WP User ID: 5
[2025-09-25 15:39:12] [961914011712]Customer exists, WP User ID: 4
[2025-09-25 15:39:12] [1101518143552]Customer exists, WP User ID: 5