BaseX XQuery is slow (again!) - basex

Question

Years ago, we had problems with an XQuery. See here:
BaseX: Slow XQuery
We were able to solve the issue with the help of the community (string literal required for index to operate properly). But now (suddently) the very same query is slow again!
The query xquery /*:ARTICLE/*:ART[*:PRDNO='1104423'] takes ~3-30s (XML file is ~500MB), same with xquery count(/*:ARTICLE/*:ART[*:PRDNO='1104423']).
Result from info database is unsuspicious, there is a text index.
I set "QUERYPLAN", "XMLPLAN" and "COMPPLAN" to true.
This gives the following for the "count" query:
Query plan:
<QueryPlan compiled="true">
<FnCount name="count(items)">
<IterPath>
<Root/>
<IterStep axis="child" test="*:ARTICLE"/>
<IterStep axis="child" test="*:ART">
<CmpG op="=">
<CachedPath>
<IterStep axis="child" test="*:PRDNO"/>
</CachedPath>
<Str value="1104423" type="xs:string"/>
</CmpG>
</IterStep>
</IterPath>
</FnCount>
</QueryPlan>
Query:
count(/*:ARTICLE/*:ART[*:PRDNO='1104423'])
Parsing: 0.21 ms
Compiling: 0.27 ms
Evaluating: 28453.24 ms
Printing: 0.15 ms
Total Time: 28453.87 ms
Hit(s): 1 Item
Updated: 0 Items
Printed: 1 b
Read Locking: hospindex
Write Locking: (none)
Query executed in 28453.87 ms.
Similarly, this is what I get for the query without "count":
Query plan:
<QueryPlan compiled="true">
<IterPath>
<Root/>
<IterStep axis="child" test="*:ARTICLE"/>
<IterStep axis="child" test="*:ART">
<CmpG op="=">
<CachedPath>
<IterStep axis="child" test="*:PRDNO"/>
</CachedPath>
<Str value="1104423" type="xs:string"/>
</CmpG>
</IterStep>
</IterPath>
</QueryPlan>
Query:
/*:ARTICLE/*:ART[*:PRDNO='1104423']
Parsing: 0.02 ms
Compiling: 0.01 ms
Evaluating: 0.49 ms
Printing: 20093.88 ms
Total Time: 20094.41 ms
Hit(s): 1 Item
Updated: 0 Items
Printed: 1583 b
Read Locking: hospindex
Write Locking: (none)
Query executed in 20094.41 ms.
Interestingly, the "print" time is very high, but the result which is printed only has a few rows.
We have recreated and optimized the database.
The query plan looks as if the index was used, right?
Any advice? Thank you very much!