Based on the provided process variants and their frequencies and performances, here are some root causes for the performance issues:

1. **Multiple Rejections and Resubmissions**: Many variants involve multiple rejections and resubmissions, which significantly increase the processing time. This is evident in variants where the declaration is rejected by ADMINISTRATION, PRE_APPROVER, SUPERVISOR, or BUDGET OWNER, and then resubmitted by the EMPLOYEE. Examples include:
   - Variant with frequency 345 (performance = 1604595.638)
   - Variant with frequency 188 (performance = 2061236.516)
   - Variant with frequency 36 (performance = 2542497.917)

2. **Involvement of Multiple Approvers**: Variants that involve multiple approvers (ADMINISTRATION, BUDGET OWNER, SUPERVISOR, PRE_APPROVER) tend to have higher processing times. This suggests that the number of approval steps impacts performance. Examples include:
   - Variant with frequency 2473 (performance = 1084338.407)
   - Variant with frequency 49 (performance = 1685420.041)

3. **Missing Information**: Variants where declarations are rejected due to missing information also contribute to performance issues. This is seen in:
   - Variant with frequency 40 (performance = 1947246.400)
   - Variant with frequency 7 (performance = 4922455.714)

4. **High Frequency of Low-Performance Variants**: Some variants with relatively high frequencies have significantly higher processing times compared to the most frequent variant. For example:
   - Variant with frequency 2473 (performance = 1084338.407) compared to the variant with frequency 4618 (performance = 810187.903)

5. **Outliers with Extremely High Performance Issues**: Some low-frequency variants have extremely high performance values, indicating significant process issues. Examples include:
   - Variant with frequency 5 (performance = 13805869.200)
   - Variant with frequency 4 (performance = 3502608.250)

Addressing these specific issues, such as reducing rejections, streamlining approvals, ensuring complete information, and investigating outliers, could help improve the overall process performance.