I looked at the game logs for 2017, and he stayed pretty steady for 4 moths, then he fell the last 2.
Here's his cumulative OPS every 1st and 15th of the month. (Note: as the season progresses the numbers go up and down with much more difficulty.)
.971
.931
.849
.931
.894
.937
.878
.918
.873
.853
.859
.818
(pretty consistent up to SEP 15th)
Now, the 8th and 22nd of every month
.786 (after 4 games)
.931
.931 (missed games from April 20-May 11)
.847
.945
.892
.897
.901
.906
.876
.864
.830
Duda played in 127 games this year. How many times did his OPS fall for...
9 straight games? 1 (end of SEP, which included one game going down .001 and another .002 with an 0-1 game) (5 for 37)
7 straight? 1 (which included a game he went 2 for 5, but his OPS was so high and .800 game OPS hurt him!)
6 straight games? 1 (1 for 19 stretch)
5 straight games? 1 (0 for 12 stretch that included an 0-1 game)
4 straight games? 2
3 straight games? 7
I just don't see many prolonged slumps in 2017, except for his last 11 games of 2017 (4 for 39). Or, his last 15 games at 6 for 52.
Cherry-picking a few others, I found...
15 games (Aug 17-SEP 4) 5 for 47 with 4 HRs
12 games (APR 16-May 21st with injury in middle and 2 zero for one games)
4 for 33 with 0 HRs (basically a 10 games slump)
10 games (Jun7 to Jun 17 including an 0-1 game and a 1 for 2 game with a BB)
3 for 32 (basically a 9 game slump)
6 games (JUL2-JUL9)
1 for 16 (hardly enough to call a real slump)
5 games (AUG8-AUG 14 including one 0-1 game)
0 for 15 with 2BB
Basically, from April to AUG 15th, he was pretty consistent, then he had two very bad stretches sandwiched around a 4 games stretch of going 5 for 14 with 3HRs
His last full season before 2017 was 2015. Here's his every 7 or 8 game cumulative OPS...
.855
.916
.896
.851
.834 (7 for 56 or .125 over 11 games, including one at 0 for 1 to go from .896 to .834)
.840
.934
.898
.878
.863
.813
.779
.772 (11 for 70 or .157 with 2 HRs in 20 games to go from from .863 to .772)
.770
.827
.822
.810
.805
.838
So, basically 2 bad slumps of 11 and 20 games with the rest being remarkably consistent and good.
I've seem much streakier hitters than Duda,