I would expect the second issue you're seeing because the creation of the cursor has no effect on the source data. I would also assume that the count you're getting for the first cursor is wrong unless your data happens to match the filter in the cursor. Have you tried creating a feature layer against the data using the filters you're providing to the cursor? Otherwise you can iterate through the cursor and get the count prior to looping through it again. I wrote up examples of this below, but note I didn't test either of these. They're just how I'm thinking this would work.
Option A - Get the count using a table view or feature layer
ufields = ("STREAM_CODE","SPECSTR","TYPE","MEAS","PROB")
ufilter = "TYPE = 'MIDSP'"
with arcpy.da.UpdateCursor(inPtMeasureTbl, ufields, ufilter) as ucursor:
utview = arcpy.management.MakeTableView(inPtMeasureTbl, "utable", ufilter)
ucount = int(arcpy.management.GetCount(uview).getOutput(0))
for urow in ucursor:
cfields = ("STREAM_CODE","SPECLS","F_MEAS","T_MEAS")
cfilter = "STREAM_CODE='{}' and F_MEAS <= {:.6f} and T_MEAS >= {:.6f}".format(*[urow[0], urow[3], urow[3]])
with arcpy.da.SearchCursor(inEventTbl, cfields, cfilter) as ccursor:
ctview = arcpy.management.MakeTableView(inEventTbl, "ctable", cfilter)
ccount = int(arcpy.management.GetCount(ctview).getOutput(0))
print("Line Events Count: {0}".format(count))
for crow in ccursor:
print("Found event: {} Specstr: {} Measures: {:.6f} , {:.6f}".format(*row))
Option B - Get the count from the cursor
ufields = ("STREAM_CODE","SPECSTR","TYPE","MEAS","PROB")
ufilter = "TYPE = 'MIDSP'"
with arcpy.da.UpdateCursor(inPtMeasureTbl, ufields, ufilter) as ucursor:
ucount = 0
for _ in ucursor:
ucount += 1
ucursor.reset()
for urow in ucursor:
cfields = ("STREAM_CODE","SPECLS","F_MEAS","T_MEAS")
cfilter = "STREAM_CODE='{}' and F_MEAS <= {:.6f} and T_MEAS >= {:.6f}".format(*[urow[0], urow[3], urow[3]])
with arcpy.da.SearchCursor(inEventTbl, cfields, cfilter) as ccursor:
ccount = 0
for _ in ccursor:
ccount += 1
ccursor.reset()
print("Line Events Count: {0}".format(count))
for crow in ccursor:
print("Found event: {} Specstr: {} Measures: {:.6f} , {:.6f}".format(*row))