So the two types of aggregation that can occur are "growth", where peptides bump into each other and adhere into a "snowball" kind of structure, growing larger over time.
The other type of aggregation is spontaneous, where certain conditions will cause a certain size and shape to form almost immediately. with no intermediate "growth".
The latter is what I think the strings are, and most commonly the result of the PH being too acidic or base.
What may happen is the PH changes a little as the solution sits, just enough for the conditions to no longer support the spontaneous large string aggregates and they fall apart, "disaggregate" back into solution. On the other hand, the change in PH may just result in smaller, sub visible aggregates, not breaking the strings down back into rHGH monomers.
Ideal PH would prevent aggregation almost entirely.
You can see the impact of PH on types of aggregates formation here using GLP-1 as an example peptide (cloudy particles vs strings):
View attachment 340227
And the impact on rHGH. The researchers were able to reproduce conditions creating "strings" by adjusting PH:
View attachment 340225